src/HOL/Algebra/UnivPoly.thy
 author nipkow Fri Aug 28 18:52:41 2009 +0200 (2009-08-28) changeset 32436 10cd49e0c067 parent 30729 461ee3e49ad3 child 32456 341c83339aeb permissions -rw-r--r--
Turned "x <= y ==> sup x y = y" (and relatives) into simp rules
     1 (*

     2   Title:     HOL/Algebra/UnivPoly.thy

     3   Author:    Clemens Ballarin, started 9 December 1996

     4   Copyright: Clemens Ballarin

     5

     6 Contributions, in particular on long division, by Jesus Aransay.

     7 *)

     8

     9 theory UnivPoly

    10 imports Module RingHom

    11 begin

    12

    13

    14 section {* Univariate Polynomials *}

    15

    16 text {*

    17   Polynomials are formalised as modules with additional operations for

    18   extracting coefficients from polynomials and for obtaining monomials

    19   from coefficients and exponents (record @{text "up_ring"}).  The

    20   carrier set is a set of bounded functions from Nat to the

    21   coefficient domain.  Bounded means that these functions return zero

    22   above a certain bound (the degree).  There is a chapter on the

    23   formalisation of polynomials in the PhD thesis \cite{Ballarin:1999},

    24   which was implemented with axiomatic type classes.  This was later

    25   ported to Locales.

    26 *}

    27

    28

    29 subsection {* The Constructor for Univariate Polynomials *}

    30

    31 text {*

    32   Functions with finite support.

    33 *}

    34

    35 locale bound =

    36   fixes z :: 'a

    37     and n :: nat

    38     and f :: "nat => 'a"

    39   assumes bound: "!!m. n < m \<Longrightarrow> f m = z"

    40

    41 declare bound.intro [intro!]

    42   and bound.bound [dest]

    43

    44 lemma bound_below:

    45   assumes bound: "bound z m f" and nonzero: "f n \<noteq> z" shows "n \<le> m"

    46 proof (rule classical)

    47   assume "~ ?thesis"

    48   then have "m < n" by arith

    49   with bound have "f n = z" ..

    50   with nonzero show ?thesis by contradiction

    51 qed

    52

    53 record ('a, 'p) up_ring = "('a, 'p) module" +

    54   monom :: "['a, nat] => 'p"

    55   coeff :: "['p, nat] => 'a"

    56

    57 definition up :: "('a, 'm) ring_scheme => (nat => 'a) set"

    58   where up_def: "up R == {f. f \<in> UNIV -> carrier R & (EX n. bound \<zero>\<^bsub>R\<^esub> n f)}"

    59

    60 definition UP :: "('a, 'm) ring_scheme => ('a, nat => 'a) up_ring"

    61   where UP_def: "UP R == (|

    62    carrier = up R,

    63    mult = (%p:up R. %q:up R. %n. \<Oplus>\<^bsub>R\<^esub>i \<in> {..n}. p i \<otimes>\<^bsub>R\<^esub> q (n-i)),

    64    one = (%i. if i=0 then \<one>\<^bsub>R\<^esub> else \<zero>\<^bsub>R\<^esub>),

    65    zero = (%i. \<zero>\<^bsub>R\<^esub>),

    66    add = (%p:up R. %q:up R. %i. p i \<oplus>\<^bsub>R\<^esub> q i),

    67    smult = (%a:carrier R. %p:up R. %i. a \<otimes>\<^bsub>R\<^esub> p i),

    68    monom = (%a:carrier R. %n i. if i=n then a else \<zero>\<^bsub>R\<^esub>),

    69    coeff = (%p:up R. %n. p n) |)"

    70

    71 text {*

    72   Properties of the set of polynomials @{term up}.

    73 *}

    74

    75 lemma mem_upI [intro]:

    76   "[| !!n. f n \<in> carrier R; EX n. bound (zero R) n f |] ==> f \<in> up R"

    77   by (simp add: up_def Pi_def)

    78

    79 lemma mem_upD [dest]:

    80   "f \<in> up R ==> f n \<in> carrier R"

    81   by (simp add: up_def Pi_def)

    82

    83 context ring

    84 begin

    85

    86 lemma bound_upD [dest]: "f \<in> up R ==> EX n. bound \<zero> n f" by (simp add: up_def)

    87

    88 lemma up_one_closed: "(%n. if n = 0 then \<one> else \<zero>) \<in> up R" using up_def by force

    89

    90 lemma up_smult_closed: "[| a \<in> carrier R; p \<in> up R |] ==> (%i. a \<otimes> p i) \<in> up R" by force

    91

    92 lemma up_add_closed:

    93   "[| p \<in> up R; q \<in> up R |] ==> (%i. p i \<oplus> q i) \<in> up R"

    94 proof

    95   fix n

    96   assume "p \<in> up R" and "q \<in> up R"

    97   then show "p n \<oplus> q n \<in> carrier R"

    98     by auto

    99 next

   100   assume UP: "p \<in> up R" "q \<in> up R"

   101   show "EX n. bound \<zero> n (%i. p i \<oplus> q i)"

   102   proof -

   103     from UP obtain n where boundn: "bound \<zero> n p" by fast

   104     from UP obtain m where boundm: "bound \<zero> m q" by fast

   105     have "bound \<zero> (max n m) (%i. p i \<oplus> q i)"

   106     proof

   107       fix i

   108       assume "max n m < i"

   109       with boundn and boundm and UP show "p i \<oplus> q i = \<zero>" by fastsimp

   110     qed

   111     then show ?thesis ..

   112   qed

   113 qed

   114

   115 lemma up_a_inv_closed:

   116   "p \<in> up R ==> (%i. \<ominus> (p i)) \<in> up R"

   117 proof

   118   assume R: "p \<in> up R"

   119   then obtain n where "bound \<zero> n p" by auto

   120   then have "bound \<zero> n (%i. \<ominus> p i)" by auto

   121   then show "EX n. bound \<zero> n (%i. \<ominus> p i)" by auto

   122 qed auto

   123

   124 lemma up_minus_closed:

   125   "[| p \<in> up R; q \<in> up R |] ==> (%i. p i \<ominus> q i) \<in> up R"

   126   using mem_upD [of p R] mem_upD [of q R] up_add_closed up_a_inv_closed a_minus_def [of _ R]

   127   by auto

   128

   129 lemma up_mult_closed:

   130   "[| p \<in> up R; q \<in> up R |] ==>

   131   (%n. \<Oplus>i \<in> {..n}. p i \<otimes> q (n-i)) \<in> up R"

   132 proof

   133   fix n

   134   assume "p \<in> up R" "q \<in> up R"

   135   then show "(\<Oplus>i \<in> {..n}. p i \<otimes> q (n-i)) \<in> carrier R"

   136     by (simp add: mem_upD  funcsetI)

   137 next

   138   assume UP: "p \<in> up R" "q \<in> up R"

   139   show "EX n. bound \<zero> n (%n. \<Oplus>i \<in> {..n}. p i \<otimes> q (n-i))"

   140   proof -

   141     from UP obtain n where boundn: "bound \<zero> n p" by fast

   142     from UP obtain m where boundm: "bound \<zero> m q" by fast

   143     have "bound \<zero> (n + m) (%n. \<Oplus>i \<in> {..n}. p i \<otimes> q (n - i))"

   144     proof

   145       fix k assume bound: "n + m < k"

   146       {

   147         fix i

   148         have "p i \<otimes> q (k-i) = \<zero>"

   149         proof (cases "n < i")

   150           case True

   151           with boundn have "p i = \<zero>" by auto

   152           moreover from UP have "q (k-i) \<in> carrier R" by auto

   153           ultimately show ?thesis by simp

   154         next

   155           case False

   156           with bound have "m < k-i" by arith

   157           with boundm have "q (k-i) = \<zero>" by auto

   158           moreover from UP have "p i \<in> carrier R" by auto

   159           ultimately show ?thesis by simp

   160         qed

   161       }

   162       then show "(\<Oplus>i \<in> {..k}. p i \<otimes> q (k-i)) = \<zero>"

   163         by (simp add: Pi_def)

   164     qed

   165     then show ?thesis by fast

   166   qed

   167 qed

   168

   169 end

   170

   171

   172 subsection {* Effect of Operations on Coefficients *}

   173

   174 locale UP =

   175   fixes R (structure) and P (structure)

   176   defines P_def: "P == UP R"

   177

   178 locale UP_ring = UP + R: ring R

   179

   180 locale UP_cring = UP + R: cring R

   181

   182 sublocale UP_cring < UP_ring

   183   by intro_locales  (rule P_def)

   184

   185 locale UP_domain = UP + R: "domain" R

   186

   187 sublocale UP_domain < UP_cring

   188   by intro_locales  (rule P_def)

   189

   190 context UP

   191 begin

   192

   193 text {*Temporarily declare @{thm P_def} as simp rule.*}

   194

   195 declare P_def [simp]

   196

   197 lemma up_eqI:

   198   assumes prem: "!!n. coeff P p n = coeff P q n" and R: "p \<in> carrier P" "q \<in> carrier P"

   199   shows "p = q"

   200 proof

   201   fix x

   202   from prem and R show "p x = q x" by (simp add: UP_def)

   203 qed

   204

   205 lemma coeff_closed [simp]:

   206   "p \<in> carrier P ==> coeff P p n \<in> carrier R" by (auto simp add: UP_def)

   207

   208 end

   209

   210 context UP_ring

   211 begin

   212

   213 (* Theorems generalised from commutative rings to rings by Jesus Aransay. *)

   214

   215 lemma coeff_monom [simp]:

   216   "a \<in> carrier R ==> coeff P (monom P a m) n = (if m=n then a else \<zero>)"

   217 proof -

   218   assume R: "a \<in> carrier R"

   219   then have "(%n. if n = m then a else \<zero>) \<in> up R"

   220     using up_def by force

   221   with R show ?thesis by (simp add: UP_def)

   222 qed

   223

   224 lemma coeff_zero [simp]: "coeff P \<zero>\<^bsub>P\<^esub> n = \<zero>" by (auto simp add: UP_def)

   225

   226 lemma coeff_one [simp]: "coeff P \<one>\<^bsub>P\<^esub> n = (if n=0 then \<one> else \<zero>)"

   227   using up_one_closed by (simp add: UP_def)

   228

   229 lemma coeff_smult [simp]:

   230   "[| a \<in> carrier R; p \<in> carrier P |] ==> coeff P (a \<odot>\<^bsub>P\<^esub> p) n = a \<otimes> coeff P p n"

   231   by (simp add: UP_def up_smult_closed)

   232

   233 lemma coeff_add [simp]:

   234   "[| p \<in> carrier P; q \<in> carrier P |] ==> coeff P (p \<oplus>\<^bsub>P\<^esub> q) n = coeff P p n \<oplus> coeff P q n"

   235   by (simp add: UP_def up_add_closed)

   236

   237 lemma coeff_mult [simp]:

   238   "[| p \<in> carrier P; q \<in> carrier P |] ==> coeff P (p \<otimes>\<^bsub>P\<^esub> q) n = (\<Oplus>i \<in> {..n}. coeff P p i \<otimes> coeff P q (n-i))"

   239   by (simp add: UP_def up_mult_closed)

   240

   241 end

   242

   243

   244 subsection {* Polynomials Form a Ring. *}

   245

   246 context UP_ring

   247 begin

   248

   249 text {* Operations are closed over @{term P}. *}

   250

   251 lemma UP_mult_closed [simp]:

   252   "[| p \<in> carrier P; q \<in> carrier P |] ==> p \<otimes>\<^bsub>P\<^esub> q \<in> carrier P" by (simp add: UP_def up_mult_closed)

   253

   254 lemma UP_one_closed [simp]:

   255   "\<one>\<^bsub>P\<^esub> \<in> carrier P" by (simp add: UP_def up_one_closed)

   256

   257 lemma UP_zero_closed [intro, simp]:

   258   "\<zero>\<^bsub>P\<^esub> \<in> carrier P" by (auto simp add: UP_def)

   259

   260 lemma UP_a_closed [intro, simp]:

   261   "[| p \<in> carrier P; q \<in> carrier P |] ==> p \<oplus>\<^bsub>P\<^esub> q \<in> carrier P" by (simp add: UP_def up_add_closed)

   262

   263 lemma monom_closed [simp]:

   264   "a \<in> carrier R ==> monom P a n \<in> carrier P" by (auto simp add: UP_def up_def Pi_def)

   265

   266 lemma UP_smult_closed [simp]:

   267   "[| a \<in> carrier R; p \<in> carrier P |] ==> a \<odot>\<^bsub>P\<^esub> p \<in> carrier P" by (simp add: UP_def up_smult_closed)

   268

   269 end

   270

   271 declare (in UP) P_def [simp del]

   272

   273 text {* Algebraic ring properties *}

   274

   275 context UP_ring

   276 begin

   277

   278 lemma UP_a_assoc:

   279   assumes R: "p \<in> carrier P" "q \<in> carrier P" "r \<in> carrier P"

   280   shows "(p \<oplus>\<^bsub>P\<^esub> q) \<oplus>\<^bsub>P\<^esub> r = p \<oplus>\<^bsub>P\<^esub> (q \<oplus>\<^bsub>P\<^esub> r)" by (rule up_eqI, simp add: a_assoc R, simp_all add: R)

   281

   282 lemma UP_l_zero [simp]:

   283   assumes R: "p \<in> carrier P"

   284   shows "\<zero>\<^bsub>P\<^esub> \<oplus>\<^bsub>P\<^esub> p = p" by (rule up_eqI, simp_all add: R)

   285

   286 lemma UP_l_neg_ex:

   287   assumes R: "p \<in> carrier P"

   288   shows "EX q : carrier P. q \<oplus>\<^bsub>P\<^esub> p = \<zero>\<^bsub>P\<^esub>"

   289 proof -

   290   let ?q = "%i. \<ominus> (p i)"

   291   from R have closed: "?q \<in> carrier P"

   292     by (simp add: UP_def P_def up_a_inv_closed)

   293   from R have coeff: "!!n. coeff P ?q n = \<ominus> (coeff P p n)"

   294     by (simp add: UP_def P_def up_a_inv_closed)

   295   show ?thesis

   296   proof

   297     show "?q \<oplus>\<^bsub>P\<^esub> p = \<zero>\<^bsub>P\<^esub>"

   298       by (auto intro!: up_eqI simp add: R closed coeff R.l_neg)

   299   qed (rule closed)

   300 qed

   301

   302 lemma UP_a_comm:

   303   assumes R: "p \<in> carrier P" "q \<in> carrier P"

   304   shows "p \<oplus>\<^bsub>P\<^esub> q = q \<oplus>\<^bsub>P\<^esub> p" by (rule up_eqI, simp add: a_comm R, simp_all add: R)

   305

   306 lemma UP_m_assoc:

   307   assumes R: "p \<in> carrier P" "q \<in> carrier P" "r \<in> carrier P"

   308   shows "(p \<otimes>\<^bsub>P\<^esub> q) \<otimes>\<^bsub>P\<^esub> r = p \<otimes>\<^bsub>P\<^esub> (q \<otimes>\<^bsub>P\<^esub> r)"

   309 proof (rule up_eqI)

   310   fix n

   311   {

   312     fix k and a b c :: "nat=>'a"

   313     assume R: "a \<in> UNIV -> carrier R" "b \<in> UNIV -> carrier R"

   314       "c \<in> UNIV -> carrier R"

   315     then have "k <= n ==>

   316       (\<Oplus>j \<in> {..k}. (\<Oplus>i \<in> {..j}. a i \<otimes> b (j-i)) \<otimes> c (n-j)) =

   317       (\<Oplus>j \<in> {..k}. a j \<otimes> (\<Oplus>i \<in> {..k-j}. b i \<otimes> c (n-j-i)))"

   318       (is "_ \<Longrightarrow> ?eq k")

   319     proof (induct k)

   320       case 0 then show ?case by (simp add: Pi_def m_assoc)

   321     next

   322       case (Suc k)

   323       then have "k <= n" by arith

   324       from this R have "?eq k" by (rule Suc)

   325       with R show ?case

   326         by (simp cong: finsum_cong

   327              add: Suc_diff_le Pi_def l_distr r_distr m_assoc)

   328            (simp cong: finsum_cong add: Pi_def a_ac finsum_ldistr m_assoc)

   329     qed

   330   }

   331   with R show "coeff P ((p \<otimes>\<^bsub>P\<^esub> q) \<otimes>\<^bsub>P\<^esub> r) n = coeff P (p \<otimes>\<^bsub>P\<^esub> (q \<otimes>\<^bsub>P\<^esub> r)) n"

   332     by (simp add: Pi_def)

   333 qed (simp_all add: R)

   334

   335 lemma UP_r_one [simp]:

   336   assumes R: "p \<in> carrier P" shows "p \<otimes>\<^bsub>P\<^esub> \<one>\<^bsub>P\<^esub> = p"

   337 proof (rule up_eqI)

   338   fix n

   339   show "coeff P (p \<otimes>\<^bsub>P\<^esub> \<one>\<^bsub>P\<^esub>) n = coeff P p n"

   340   proof (cases n)

   341     case 0

   342     {

   343       with R show ?thesis by simp

   344     }

   345   next

   346     case Suc

   347     {

   348       (*JE: in the locale UP_cring the proof was solved only with "by (simp del: finsum_Suc add: finsum_Suc2 Pi_def)", but I did not get it to work here*)

   349       fix nn assume Succ: "n = Suc nn"

   350       have "coeff P (p \<otimes>\<^bsub>P\<^esub> \<one>\<^bsub>P\<^esub>) (Suc nn) = coeff P p (Suc nn)"

   351       proof -

   352 	have "coeff P (p \<otimes>\<^bsub>P\<^esub> \<one>\<^bsub>P\<^esub>) (Suc nn) = (\<Oplus>i\<in>{..Suc nn}. coeff P p i \<otimes> (if Suc nn \<le> i then \<one> else \<zero>))" using R by simp

   353 	also have "\<dots> = coeff P p (Suc nn) \<otimes> (if Suc nn \<le> Suc nn then \<one> else \<zero>) \<oplus> (\<Oplus>i\<in>{..nn}. coeff P p i \<otimes> (if Suc nn \<le> i then \<one> else \<zero>))"

   354 	  using finsum_Suc [of "(\<lambda>i::nat. coeff P p i \<otimes> (if Suc nn \<le> i then \<one> else \<zero>))" "nn"] unfolding Pi_def using R by simp

   355 	also have "\<dots> = coeff P p (Suc nn) \<otimes> (if Suc nn \<le> Suc nn then \<one> else \<zero>)"

   356 	proof -

   357 	  have "(\<Oplus>i\<in>{..nn}. coeff P p i \<otimes> (if Suc nn \<le> i then \<one> else \<zero>)) = (\<Oplus>i\<in>{..nn}. \<zero>)"

   358 	    using finsum_cong [of "{..nn}" "{..nn}" "(\<lambda>i::nat. coeff P p i \<otimes> (if Suc nn \<le> i then \<one> else \<zero>))" "(\<lambda>i::nat. \<zero>)"] using R

   359 	    unfolding Pi_def by simp

   360 	  also have "\<dots> = \<zero>" by simp

   361 	  finally show ?thesis using r_zero R by simp

   362 	qed

   363 	also have "\<dots> = coeff P p (Suc nn)" using R by simp

   364 	finally show ?thesis by simp

   365       qed

   366       then show ?thesis using Succ by simp

   367     }

   368   qed

   369 qed (simp_all add: R)

   370

   371 lemma UP_l_one [simp]:

   372   assumes R: "p \<in> carrier P"

   373   shows "\<one>\<^bsub>P\<^esub> \<otimes>\<^bsub>P\<^esub> p = p"

   374 proof (rule up_eqI)

   375   fix n

   376   show "coeff P (\<one>\<^bsub>P\<^esub> \<otimes>\<^bsub>P\<^esub> p) n = coeff P p n"

   377   proof (cases n)

   378     case 0 with R show ?thesis by simp

   379   next

   380     case Suc with R show ?thesis

   381       by (simp del: finsum_Suc add: finsum_Suc2 Pi_def)

   382   qed

   383 qed (simp_all add: R)

   384

   385 lemma UP_l_distr:

   386   assumes R: "p \<in> carrier P" "q \<in> carrier P" "r \<in> carrier P"

   387   shows "(p \<oplus>\<^bsub>P\<^esub> q) \<otimes>\<^bsub>P\<^esub> r = (p \<otimes>\<^bsub>P\<^esub> r) \<oplus>\<^bsub>P\<^esub> (q \<otimes>\<^bsub>P\<^esub> r)"

   388   by (rule up_eqI) (simp add: l_distr R Pi_def, simp_all add: R)

   389

   390 lemma UP_r_distr:

   391   assumes R: "p \<in> carrier P" "q \<in> carrier P" "r \<in> carrier P"

   392   shows "r \<otimes>\<^bsub>P\<^esub> (p \<oplus>\<^bsub>P\<^esub> q) = (r \<otimes>\<^bsub>P\<^esub> p) \<oplus>\<^bsub>P\<^esub> (r \<otimes>\<^bsub>P\<^esub> q)"

   393   by (rule up_eqI) (simp add: r_distr R Pi_def, simp_all add: R)

   394

   395 theorem UP_ring: "ring P"

   396   by (auto intro!: ringI abelian_groupI monoidI UP_a_assoc)

   397     (auto intro: UP_a_comm UP_l_neg_ex UP_m_assoc UP_l_distr UP_r_distr)

   398

   399 end

   400

   401

   402 subsection {* Polynomials Form a Commutative Ring. *}

   403

   404 context UP_cring

   405 begin

   406

   407 lemma UP_m_comm:

   408   assumes R1: "p \<in> carrier P" and R2: "q \<in> carrier P" shows "p \<otimes>\<^bsub>P\<^esub> q = q \<otimes>\<^bsub>P\<^esub> p"

   409 proof (rule up_eqI)

   410   fix n

   411   {

   412     fix k and a b :: "nat=>'a"

   413     assume R: "a \<in> UNIV -> carrier R" "b \<in> UNIV -> carrier R"

   414     then have "k <= n ==>

   415       (\<Oplus>i \<in> {..k}. a i \<otimes> b (n-i)) = (\<Oplus>i \<in> {..k}. a (k-i) \<otimes> b (i+n-k))"

   416       (is "_ \<Longrightarrow> ?eq k")

   417     proof (induct k)

   418       case 0 then show ?case by (simp add: Pi_def)

   419     next

   420       case (Suc k) then show ?case

   421         by (subst (2) finsum_Suc2) (simp add: Pi_def a_comm)+

   422     qed

   423   }

   424   note l = this

   425   from R1 R2 show "coeff P (p \<otimes>\<^bsub>P\<^esub> q) n =  coeff P (q \<otimes>\<^bsub>P\<^esub> p) n"

   426     unfolding coeff_mult [OF R1 R2, of n]

   427     unfolding coeff_mult [OF R2 R1, of n]

   428     using l [of "(\<lambda>i. coeff P p i)" "(\<lambda>i. coeff P q i)" "n"] by (simp add: Pi_def m_comm)

   429 qed (simp_all add: R1 R2)

   430

   431 subsection{*Polynomials over a commutative ring for a commutative ring*}

   432

   433 theorem UP_cring:

   434   "cring P" using UP_ring unfolding cring_def by (auto intro!: comm_monoidI UP_m_assoc UP_m_comm)

   435

   436 end

   437

   438 context UP_ring

   439 begin

   440

   441 lemma UP_a_inv_closed [intro, simp]:

   442   "p \<in> carrier P ==> \<ominus>\<^bsub>P\<^esub> p \<in> carrier P"

   443   by (rule abelian_group.a_inv_closed [OF ring.is_abelian_group [OF UP_ring]])

   444

   445 lemma coeff_a_inv [simp]:

   446   assumes R: "p \<in> carrier P"

   447   shows "coeff P (\<ominus>\<^bsub>P\<^esub> p) n = \<ominus> (coeff P p n)"

   448 proof -

   449   from R coeff_closed UP_a_inv_closed have

   450     "coeff P (\<ominus>\<^bsub>P\<^esub> p) n = \<ominus> coeff P p n \<oplus> (coeff P p n \<oplus> coeff P (\<ominus>\<^bsub>P\<^esub> p) n)"

   451     by algebra

   452   also from R have "... =  \<ominus> (coeff P p n)"

   453     by (simp del: coeff_add add: coeff_add [THEN sym]

   454       abelian_group.r_neg [OF ring.is_abelian_group [OF UP_ring]])

   455   finally show ?thesis .

   456 qed

   457

   458 end

   459

   460 sublocale UP_ring < P: ring P using UP_ring .

   461 sublocale UP_cring < P: cring P using UP_cring .

   462

   463

   464 subsection {* Polynomials Form an Algebra *}

   465

   466 context UP_ring

   467 begin

   468

   469 lemma UP_smult_l_distr:

   470   "[| a \<in> carrier R; b \<in> carrier R; p \<in> carrier P |] ==>

   471   (a \<oplus> b) \<odot>\<^bsub>P\<^esub> p = a \<odot>\<^bsub>P\<^esub> p \<oplus>\<^bsub>P\<^esub> b \<odot>\<^bsub>P\<^esub> p"

   472   by (rule up_eqI) (simp_all add: R.l_distr)

   473

   474 lemma UP_smult_r_distr:

   475   "[| a \<in> carrier R; p \<in> carrier P; q \<in> carrier P |] ==>

   476   a \<odot>\<^bsub>P\<^esub> (p \<oplus>\<^bsub>P\<^esub> q) = a \<odot>\<^bsub>P\<^esub> p \<oplus>\<^bsub>P\<^esub> a \<odot>\<^bsub>P\<^esub> q"

   477   by (rule up_eqI) (simp_all add: R.r_distr)

   478

   479 lemma UP_smult_assoc1:

   480       "[| a \<in> carrier R; b \<in> carrier R; p \<in> carrier P |] ==>

   481       (a \<otimes> b) \<odot>\<^bsub>P\<^esub> p = a \<odot>\<^bsub>P\<^esub> (b \<odot>\<^bsub>P\<^esub> p)"

   482   by (rule up_eqI) (simp_all add: R.m_assoc)

   483

   484 lemma UP_smult_zero [simp]:

   485       "p \<in> carrier P ==> \<zero> \<odot>\<^bsub>P\<^esub> p = \<zero>\<^bsub>P\<^esub>"

   486   by (rule up_eqI) simp_all

   487

   488 lemma UP_smult_one [simp]:

   489       "p \<in> carrier P ==> \<one> \<odot>\<^bsub>P\<^esub> p = p"

   490   by (rule up_eqI) simp_all

   491

   492 lemma UP_smult_assoc2:

   493   "[| a \<in> carrier R; p \<in> carrier P; q \<in> carrier P |] ==>

   494   (a \<odot>\<^bsub>P\<^esub> p) \<otimes>\<^bsub>P\<^esub> q = a \<odot>\<^bsub>P\<^esub> (p \<otimes>\<^bsub>P\<^esub> q)"

   495   by (rule up_eqI) (simp_all add: R.finsum_rdistr R.m_assoc Pi_def)

   496

   497 end

   498

   499 text {*

   500   Interpretation of lemmas from @{term algebra}.

   501 *}

   502

   503 lemma (in cring) cring:

   504   "cring R" ..

   505

   506 lemma (in UP_cring) UP_algebra:

   507   "algebra R P" by (auto intro!: algebraI R.cring UP_cring UP_smult_l_distr UP_smult_r_distr

   508     UP_smult_assoc1 UP_smult_assoc2)

   509

   510 sublocale UP_cring < algebra R P using UP_algebra .

   511

   512

   513 subsection {* Further Lemmas Involving Monomials *}

   514

   515 context UP_ring

   516 begin

   517

   518 lemma monom_zero [simp]:

   519   "monom P \<zero> n = \<zero>\<^bsub>P\<^esub>" by (simp add: UP_def P_def)

   520

   521 lemma monom_mult_is_smult:

   522   assumes R: "a \<in> carrier R" "p \<in> carrier P"

   523   shows "monom P a 0 \<otimes>\<^bsub>P\<^esub> p = a \<odot>\<^bsub>P\<^esub> p"

   524 proof (rule up_eqI)

   525   fix n

   526   show "coeff P (monom P a 0 \<otimes>\<^bsub>P\<^esub> p) n = coeff P (a \<odot>\<^bsub>P\<^esub> p) n"

   527   proof (cases n)

   528     case 0 with R show ?thesis by simp

   529   next

   530     case Suc with R show ?thesis

   531       using R.finsum_Suc2 by (simp del: R.finsum_Suc add: R.r_null Pi_def)

   532   qed

   533 qed (simp_all add: R)

   534

   535 lemma monom_one [simp]:

   536   "monom P \<one> 0 = \<one>\<^bsub>P\<^esub>"

   537   by (rule up_eqI) simp_all

   538

   539 lemma monom_add [simp]:

   540   "[| a \<in> carrier R; b \<in> carrier R |] ==>

   541   monom P (a \<oplus> b) n = monom P a n \<oplus>\<^bsub>P\<^esub> monom P b n"

   542   by (rule up_eqI) simp_all

   543

   544 lemma monom_one_Suc:

   545   "monom P \<one> (Suc n) = monom P \<one> n \<otimes>\<^bsub>P\<^esub> monom P \<one> 1"

   546 proof (rule up_eqI)

   547   fix k

   548   show "coeff P (monom P \<one> (Suc n)) k = coeff P (monom P \<one> n \<otimes>\<^bsub>P\<^esub> monom P \<one> 1) k"

   549   proof (cases "k = Suc n")

   550     case True show ?thesis

   551     proof -

   552       fix m

   553       from True have less_add_diff:

   554         "!!i. [| n < i; i <= n + m |] ==> n + m - i < m" by arith

   555       from True have "coeff P (monom P \<one> (Suc n)) k = \<one>" by simp

   556       also from True

   557       have "... = (\<Oplus>i \<in> {..<n} \<union> {n}. coeff P (monom P \<one> n) i \<otimes>

   558         coeff P (monom P \<one> 1) (k - i))"

   559         by (simp cong: R.finsum_cong add: Pi_def)

   560       also have "... = (\<Oplus>i \<in>  {..n}. coeff P (monom P \<one> n) i \<otimes>

   561         coeff P (monom P \<one> 1) (k - i))"

   562         by (simp only: ivl_disj_un_singleton)

   563       also from True

   564       have "... = (\<Oplus>i \<in> {..n} \<union> {n<..k}. coeff P (monom P \<one> n) i \<otimes>

   565         coeff P (monom P \<one> 1) (k - i))"

   566         by (simp cong: R.finsum_cong add: R.finsum_Un_disjoint ivl_disj_int_one

   567           order_less_imp_not_eq Pi_def)

   568       also from True have "... = coeff P (monom P \<one> n \<otimes>\<^bsub>P\<^esub> monom P \<one> 1) k"

   569         by (simp add: ivl_disj_un_one)

   570       finally show ?thesis .

   571     qed

   572   next

   573     case False

   574     note neq = False

   575     let ?s =

   576       "\<lambda>i. (if n = i then \<one> else \<zero>) \<otimes> (if Suc 0 = k - i then \<one> else \<zero>)"

   577     from neq have "coeff P (monom P \<one> (Suc n)) k = \<zero>" by simp

   578     also have "... = (\<Oplus>i \<in> {..k}. ?s i)"

   579     proof -

   580       have f1: "(\<Oplus>i \<in> {..<n}. ?s i) = \<zero>"

   581         by (simp cong: R.finsum_cong add: Pi_def)

   582       from neq have f2: "(\<Oplus>i \<in> {n}. ?s i) = \<zero>"

   583         by (simp cong: R.finsum_cong add: Pi_def) arith

   584       have f3: "n < k ==> (\<Oplus>i \<in> {n<..k}. ?s i) = \<zero>"

   585         by (simp cong: R.finsum_cong add: order_less_imp_not_eq Pi_def)

   586       show ?thesis

   587       proof (cases "k < n")

   588         case True then show ?thesis by (simp cong: R.finsum_cong add: Pi_def)

   589       next

   590         case False then have n_le_k: "n <= k" by arith

   591         show ?thesis

   592         proof (cases "n = k")

   593           case True

   594           then have "\<zero> = (\<Oplus>i \<in> {..<n} \<union> {n}. ?s i)"

   595             by (simp cong: R.finsum_cong add: ivl_disj_int_singleton Pi_def)

   596           also from True have "... = (\<Oplus>i \<in> {..k}. ?s i)"

   597             by (simp only: ivl_disj_un_singleton)

   598           finally show ?thesis .

   599         next

   600           case False with n_le_k have n_less_k: "n < k" by arith

   601           with neq have "\<zero> = (\<Oplus>i \<in> {..<n} \<union> {n}. ?s i)"

   602             by (simp add: R.finsum_Un_disjoint f1 f2

   603               ivl_disj_int_singleton Pi_def del: Un_insert_right)

   604           also have "... = (\<Oplus>i \<in> {..n}. ?s i)"

   605             by (simp only: ivl_disj_un_singleton)

   606           also from n_less_k neq have "... = (\<Oplus>i \<in> {..n} \<union> {n<..k}. ?s i)"

   607             by (simp add: R.finsum_Un_disjoint f3 ivl_disj_int_one Pi_def)

   608           also from n_less_k have "... = (\<Oplus>i \<in> {..k}. ?s i)"

   609             by (simp only: ivl_disj_un_one)

   610           finally show ?thesis .

   611         qed

   612       qed

   613     qed

   614     also have "... = coeff P (monom P \<one> n \<otimes>\<^bsub>P\<^esub> monom P \<one> 1) k" by simp

   615     finally show ?thesis .

   616   qed

   617 qed (simp_all)

   618

   619 lemma monom_one_Suc2:

   620   "monom P \<one> (Suc n) = monom P \<one> 1 \<otimes>\<^bsub>P\<^esub> monom P \<one> n"

   621 proof (induct n)

   622   case 0 show ?case by simp

   623 next

   624   case Suc

   625   {

   626     fix k:: nat

   627     assume hypo: "monom P \<one> (Suc k) = monom P \<one> 1 \<otimes>\<^bsub>P\<^esub> monom P \<one> k"

   628     then show "monom P \<one> (Suc (Suc k)) = monom P \<one> 1 \<otimes>\<^bsub>P\<^esub> monom P \<one> (Suc k)"

   629     proof -

   630       have lhs: "monom P \<one> (Suc (Suc k)) = monom P \<one> 1 \<otimes>\<^bsub>P\<^esub> monom P \<one> k \<otimes>\<^bsub>P\<^esub> monom P \<one> 1"

   631 	unfolding monom_one_Suc [of "Suc k"] unfolding hypo ..

   632       note cl = monom_closed [OF R.one_closed, of 1]

   633       note clk = monom_closed [OF R.one_closed, of k]

   634       have rhs: "monom P \<one> 1 \<otimes>\<^bsub>P\<^esub> monom P \<one> (Suc k) = monom P \<one> 1 \<otimes>\<^bsub>P\<^esub> monom P \<one> k \<otimes>\<^bsub>P\<^esub> monom P \<one> 1"

   635 	unfolding monom_one_Suc [of k] unfolding sym [OF m_assoc  [OF cl clk cl]] ..

   636       from lhs rhs show ?thesis by simp

   637     qed

   638   }

   639 qed

   640

   641 text{*The following corollary follows from lemmas @{thm "monom_one_Suc"}

   642   and @{thm "monom_one_Suc2"}, and is trivial in @{term UP_cring}*}

   643

   644 corollary monom_one_comm: shows "monom P \<one> k \<otimes>\<^bsub>P\<^esub> monom P \<one> 1 = monom P \<one> 1 \<otimes>\<^bsub>P\<^esub> monom P \<one> k"

   645   unfolding monom_one_Suc [symmetric] monom_one_Suc2 [symmetric] ..

   646

   647 lemma monom_mult_smult:

   648   "[| a \<in> carrier R; b \<in> carrier R |] ==> monom P (a \<otimes> b) n = a \<odot>\<^bsub>P\<^esub> monom P b n"

   649   by (rule up_eqI) simp_all

   650

   651 lemma monom_one_mult:

   652   "monom P \<one> (n + m) = monom P \<one> n \<otimes>\<^bsub>P\<^esub> monom P \<one> m"

   653 proof (induct n)

   654   case 0 show ?case by simp

   655 next

   656   case Suc then show ?case

   657     unfolding add_Suc unfolding monom_one_Suc unfolding Suc.hyps

   658     using m_assoc monom_one_comm [of m] by simp

   659 qed

   660

   661 lemma monom_one_mult_comm: "monom P \<one> n \<otimes>\<^bsub>P\<^esub> monom P \<one> m = monom P \<one> m \<otimes>\<^bsub>P\<^esub> monom P \<one> n"

   662   unfolding monom_one_mult [symmetric] by (rule up_eqI) simp_all

   663

   664 lemma monom_mult [simp]:

   665   assumes a_in_R: "a \<in> carrier R" and b_in_R: "b \<in> carrier R"

   666   shows "monom P (a \<otimes> b) (n + m) = monom P a n \<otimes>\<^bsub>P\<^esub> monom P b m"

   667 proof (rule up_eqI)

   668   fix k

   669   show "coeff P (monom P (a \<otimes> b) (n + m)) k = coeff P (monom P a n \<otimes>\<^bsub>P\<^esub> monom P b m) k"

   670   proof (cases "n + m = k")

   671     case True

   672     {

   673       show ?thesis

   674 	unfolding True [symmetric]

   675 	  coeff_mult [OF monom_closed [OF a_in_R, of n] monom_closed [OF b_in_R, of m], of "n + m"]

   676 	  coeff_monom [OF a_in_R, of n] coeff_monom [OF b_in_R, of m]

   677 	using R.finsum_cong [of "{.. n + m}" "{.. n + m}" "(\<lambda>i. (if n = i then a else \<zero>) \<otimes> (if m = n + m - i then b else \<zero>))"

   678 	  "(\<lambda>i. if n = i then a \<otimes> b else \<zero>)"]

   679 	  a_in_R b_in_R

   680 	unfolding simp_implies_def

   681 	using R.finsum_singleton [of n "{.. n + m}" "(\<lambda>i. a \<otimes> b)"]

   682 	unfolding Pi_def by auto

   683     }

   684   next

   685     case False

   686     {

   687       show ?thesis

   688 	unfolding coeff_monom [OF R.m_closed [OF a_in_R b_in_R], of "n + m" k] apply (simp add: False)

   689 	unfolding coeff_mult [OF monom_closed [OF a_in_R, of n] monom_closed [OF b_in_R, of m], of k]

   690 	unfolding coeff_monom [OF a_in_R, of n] unfolding coeff_monom [OF b_in_R, of m] using False

   691 	using R.finsum_cong [of "{..k}" "{..k}" "(\<lambda>i. (if n = i then a else \<zero>) \<otimes> (if m = k - i then b else \<zero>))" "(\<lambda>i. \<zero>)"]

   692 	unfolding Pi_def simp_implies_def using a_in_R b_in_R by force

   693     }

   694   qed

   695 qed (simp_all add: a_in_R b_in_R)

   696

   697 lemma monom_a_inv [simp]:

   698   "a \<in> carrier R ==> monom P (\<ominus> a) n = \<ominus>\<^bsub>P\<^esub> monom P a n"

   699   by (rule up_eqI) simp_all

   700

   701 lemma monom_inj:

   702   "inj_on (%a. monom P a n) (carrier R)"

   703 proof (rule inj_onI)

   704   fix x y

   705   assume R: "x \<in> carrier R" "y \<in> carrier R" and eq: "monom P x n = monom P y n"

   706   then have "coeff P (monom P x n) n = coeff P (monom P y n) n" by simp

   707   with R show "x = y" by simp

   708 qed

   709

   710 end

   711

   712

   713 subsection {* The Degree Function *}

   714

   715 definition deg :: "[('a, 'm) ring_scheme, nat => 'a] => nat"

   716   where "deg R p == LEAST n. bound \<zero>\<^bsub>R\<^esub> n (coeff (UP R) p)"

   717

   718 context UP_ring

   719 begin

   720

   721 lemma deg_aboveI:

   722   "[| (!!m. n < m ==> coeff P p m = \<zero>); p \<in> carrier P |] ==> deg R p <= n"

   723   by (unfold deg_def P_def) (fast intro: Least_le)

   724

   725 (*

   726 lemma coeff_bound_ex: "EX n. bound n (coeff p)"

   727 proof -

   728   have "(%n. coeff p n) : UP" by (simp add: coeff_def Rep_UP)

   729   then obtain n where "bound n (coeff p)" by (unfold UP_def) fast

   730   then show ?thesis ..

   731 qed

   732

   733 lemma bound_coeff_obtain:

   734   assumes prem: "(!!n. bound n (coeff p) ==> P)" shows "P"

   735 proof -

   736   have "(%n. coeff p n) : UP" by (simp add: coeff_def Rep_UP)

   737   then obtain n where "bound n (coeff p)" by (unfold UP_def) fast

   738   with prem show P .

   739 qed

   740 *)

   741

   742 lemma deg_aboveD:

   743   assumes "deg R p < m" and "p \<in> carrier P"

   744   shows "coeff P p m = \<zero>"

   745 proof -

   746   from p \<in> carrier P obtain n where "bound \<zero> n (coeff P p)"

   747     by (auto simp add: UP_def P_def)

   748   then have "bound \<zero> (deg R p) (coeff P p)"

   749     by (auto simp: deg_def P_def dest: LeastI)

   750   from this and deg R p < m show ?thesis ..

   751 qed

   752

   753 lemma deg_belowI:

   754   assumes non_zero: "n ~= 0 ==> coeff P p n ~= \<zero>"

   755     and R: "p \<in> carrier P"

   756   shows "n <= deg R p"

   757 -- {* Logically, this is a slightly stronger version of

   758    @{thm [source] deg_aboveD} *}

   759 proof (cases "n=0")

   760   case True then show ?thesis by simp

   761 next

   762   case False then have "coeff P p n ~= \<zero>" by (rule non_zero)

   763   then have "~ deg R p < n" by (fast dest: deg_aboveD intro: R)

   764   then show ?thesis by arith

   765 qed

   766

   767 lemma lcoeff_nonzero_deg:

   768   assumes deg: "deg R p ~= 0" and R: "p \<in> carrier P"

   769   shows "coeff P p (deg R p) ~= \<zero>"

   770 proof -

   771   from R obtain m where "deg R p <= m" and m_coeff: "coeff P p m ~= \<zero>"

   772   proof -

   773     have minus: "!!(n::nat) m. n ~= 0 ==> (n - Suc 0 < m) = (n <= m)"

   774       by arith

   775     from deg have "deg R p - 1 < (LEAST n. bound \<zero> n (coeff P p))"

   776       by (unfold deg_def P_def) simp

   777     then have "~ bound \<zero> (deg R p - 1) (coeff P p)" by (rule not_less_Least)

   778     then have "EX m. deg R p - 1 < m & coeff P p m ~= \<zero>"

   779       by (unfold bound_def) fast

   780     then have "EX m. deg R p <= m & coeff P p m ~= \<zero>" by (simp add: deg minus)

   781     then show ?thesis by (auto intro: that)

   782   qed

   783   with deg_belowI R have "deg R p = m" by fastsimp

   784   with m_coeff show ?thesis by simp

   785 qed

   786

   787 lemma lcoeff_nonzero_nonzero:

   788   assumes deg: "deg R p = 0" and nonzero: "p ~= \<zero>\<^bsub>P\<^esub>" and R: "p \<in> carrier P"

   789   shows "coeff P p 0 ~= \<zero>"

   790 proof -

   791   have "EX m. coeff P p m ~= \<zero>"

   792   proof (rule classical)

   793     assume "~ ?thesis"

   794     with R have "p = \<zero>\<^bsub>P\<^esub>" by (auto intro: up_eqI)

   795     with nonzero show ?thesis by contradiction

   796   qed

   797   then obtain m where coeff: "coeff P p m ~= \<zero>" ..

   798   from this and R have "m <= deg R p" by (rule deg_belowI)

   799   then have "m = 0" by (simp add: deg)

   800   with coeff show ?thesis by simp

   801 qed

   802

   803 lemma lcoeff_nonzero:

   804   assumes neq: "p ~= \<zero>\<^bsub>P\<^esub>" and R: "p \<in> carrier P"

   805   shows "coeff P p (deg R p) ~= \<zero>"

   806 proof (cases "deg R p = 0")

   807   case True with neq R show ?thesis by (simp add: lcoeff_nonzero_nonzero)

   808 next

   809   case False with neq R show ?thesis by (simp add: lcoeff_nonzero_deg)

   810 qed

   811

   812 lemma deg_eqI:

   813   "[| !!m. n < m ==> coeff P p m = \<zero>;

   814       !!n. n ~= 0 ==> coeff P p n ~= \<zero>; p \<in> carrier P |] ==> deg R p = n"

   815 by (fast intro: le_anti_sym deg_aboveI deg_belowI)

   816

   817 text {* Degree and polynomial operations *}

   818

   819 lemma deg_add [simp]:

   820   "p \<in> carrier P \<Longrightarrow> q \<in> carrier P \<Longrightarrow>

   821   deg R (p \<oplus>\<^bsub>P\<^esub> q) <= max (deg R p) (deg R q)"

   822 by(rule deg_aboveI)(simp_all add: deg_aboveD)

   823

   824 lemma deg_monom_le:

   825   "a \<in> carrier R ==> deg R (monom P a n) <= n"

   826   by (intro deg_aboveI) simp_all

   827

   828 lemma deg_monom [simp]:

   829   "[| a ~= \<zero>; a \<in> carrier R |] ==> deg R (monom P a n) = n"

   830   by (fastsimp intro: le_anti_sym deg_aboveI deg_belowI)

   831

   832 lemma deg_const [simp]:

   833   assumes R: "a \<in> carrier R" shows "deg R (monom P a 0) = 0"

   834 proof (rule le_anti_sym)

   835   show "deg R (monom P a 0) <= 0" by (rule deg_aboveI) (simp_all add: R)

   836 next

   837   show "0 <= deg R (monom P a 0)" by (rule deg_belowI) (simp_all add: R)

   838 qed

   839

   840 lemma deg_zero [simp]:

   841   "deg R \<zero>\<^bsub>P\<^esub> = 0"

   842 proof (rule le_anti_sym)

   843   show "deg R \<zero>\<^bsub>P\<^esub> <= 0" by (rule deg_aboveI) simp_all

   844 next

   845   show "0 <= deg R \<zero>\<^bsub>P\<^esub>" by (rule deg_belowI) simp_all

   846 qed

   847

   848 lemma deg_one [simp]:

   849   "deg R \<one>\<^bsub>P\<^esub> = 0"

   850 proof (rule le_anti_sym)

   851   show "deg R \<one>\<^bsub>P\<^esub> <= 0" by (rule deg_aboveI) simp_all

   852 next

   853   show "0 <= deg R \<one>\<^bsub>P\<^esub>" by (rule deg_belowI) simp_all

   854 qed

   855

   856 lemma deg_uminus [simp]:

   857   assumes R: "p \<in> carrier P" shows "deg R (\<ominus>\<^bsub>P\<^esub> p) = deg R p"

   858 proof (rule le_anti_sym)

   859   show "deg R (\<ominus>\<^bsub>P\<^esub> p) <= deg R p" by (simp add: deg_aboveI deg_aboveD R)

   860 next

   861   show "deg R p <= deg R (\<ominus>\<^bsub>P\<^esub> p)"

   862     by (simp add: deg_belowI lcoeff_nonzero_deg

   863       inj_on_iff [OF R.a_inv_inj, of _ "\<zero>", simplified] R)

   864 qed

   865

   866 text{*The following lemma is later \emph{overwritten} by the most

   867   specific one for domains, @{text deg_smult}.*}

   868

   869 lemma deg_smult_ring [simp]:

   870   "[| a \<in> carrier R; p \<in> carrier P |] ==>

   871   deg R (a \<odot>\<^bsub>P\<^esub> p) <= (if a = \<zero> then 0 else deg R p)"

   872   by (cases "a = \<zero>") (simp add: deg_aboveI deg_aboveD)+

   873

   874 end

   875

   876 context UP_domain

   877 begin

   878

   879 lemma deg_smult [simp]:

   880   assumes R: "a \<in> carrier R" "p \<in> carrier P"

   881   shows "deg R (a \<odot>\<^bsub>P\<^esub> p) = (if a = \<zero> then 0 else deg R p)"

   882 proof (rule le_anti_sym)

   883   show "deg R (a \<odot>\<^bsub>P\<^esub> p) <= (if a = \<zero> then 0 else deg R p)"

   884     using R by (rule deg_smult_ring)

   885 next

   886   show "(if a = \<zero> then 0 else deg R p) <= deg R (a \<odot>\<^bsub>P\<^esub> p)"

   887   proof (cases "a = \<zero>")

   888   qed (simp, simp add: deg_belowI lcoeff_nonzero_deg integral_iff R)

   889 qed

   890

   891 end

   892

   893 context UP_ring

   894 begin

   895

   896 lemma deg_mult_ring:

   897   assumes R: "p \<in> carrier P" "q \<in> carrier P"

   898   shows "deg R (p \<otimes>\<^bsub>P\<^esub> q) <= deg R p + deg R q"

   899 proof (rule deg_aboveI)

   900   fix m

   901   assume boundm: "deg R p + deg R q < m"

   902   {

   903     fix k i

   904     assume boundk: "deg R p + deg R q < k"

   905     then have "coeff P p i \<otimes> coeff P q (k - i) = \<zero>"

   906     proof (cases "deg R p < i")

   907       case True then show ?thesis by (simp add: deg_aboveD R)

   908     next

   909       case False with boundk have "deg R q < k - i" by arith

   910       then show ?thesis by (simp add: deg_aboveD R)

   911     qed

   912   }

   913   with boundm R show "coeff P (p \<otimes>\<^bsub>P\<^esub> q) m = \<zero>" by simp

   914 qed (simp add: R)

   915

   916 end

   917

   918 context UP_domain

   919 begin

   920

   921 lemma deg_mult [simp]:

   922   "[| p ~= \<zero>\<^bsub>P\<^esub>; q ~= \<zero>\<^bsub>P\<^esub>; p \<in> carrier P; q \<in> carrier P |] ==>

   923   deg R (p \<otimes>\<^bsub>P\<^esub> q) = deg R p + deg R q"

   924 proof (rule le_anti_sym)

   925   assume "p \<in> carrier P" " q \<in> carrier P"

   926   then show "deg R (p \<otimes>\<^bsub>P\<^esub> q) <= deg R p + deg R q" by (rule deg_mult_ring)

   927 next

   928   let ?s = "(%i. coeff P p i \<otimes> coeff P q (deg R p + deg R q - i))"

   929   assume R: "p \<in> carrier P" "q \<in> carrier P" and nz: "p ~= \<zero>\<^bsub>P\<^esub>" "q ~= \<zero>\<^bsub>P\<^esub>"

   930   have less_add_diff: "!!(k::nat) n m. k < n ==> m < n + m - k" by arith

   931   show "deg R p + deg R q <= deg R (p \<otimes>\<^bsub>P\<^esub> q)"

   932   proof (rule deg_belowI, simp add: R)

   933     have "(\<Oplus>i \<in> {.. deg R p + deg R q}. ?s i)

   934       = (\<Oplus>i \<in> {..< deg R p} \<union> {deg R p .. deg R p + deg R q}. ?s i)"

   935       by (simp only: ivl_disj_un_one)

   936     also have "... = (\<Oplus>i \<in> {deg R p .. deg R p + deg R q}. ?s i)"

   937       by (simp cong: R.finsum_cong add: R.finsum_Un_disjoint ivl_disj_int_one

   938         deg_aboveD less_add_diff R Pi_def)

   939     also have "...= (\<Oplus>i \<in> {deg R p} \<union> {deg R p <.. deg R p + deg R q}. ?s i)"

   940       by (simp only: ivl_disj_un_singleton)

   941     also have "... = coeff P p (deg R p) \<otimes> coeff P q (deg R q)"

   942       by (simp cong: R.finsum_cong

   943 	add: ivl_disj_int_singleton deg_aboveD R Pi_def)

   944     finally have "(\<Oplus>i \<in> {.. deg R p + deg R q}. ?s i)

   945       = coeff P p (deg R p) \<otimes> coeff P q (deg R q)" .

   946     with nz show "(\<Oplus>i \<in> {.. deg R p + deg R q}. ?s i) ~= \<zero>"

   947       by (simp add: integral_iff lcoeff_nonzero R)

   948   qed (simp add: R)

   949 qed

   950

   951 end

   952

   953 text{*The following lemmas also can be lifted to @{term UP_ring}.*}

   954

   955 context UP_ring

   956 begin

   957

   958 lemma coeff_finsum:

   959   assumes fin: "finite A"

   960   shows "p \<in> A -> carrier P ==>

   961     coeff P (finsum P p A) k = (\<Oplus>i \<in> A. coeff P (p i) k)"

   962   using fin by induct (auto simp: Pi_def)

   963

   964 lemma up_repr:

   965   assumes R: "p \<in> carrier P"

   966   shows "(\<Oplus>\<^bsub>P\<^esub> i \<in> {..deg R p}. monom P (coeff P p i) i) = p"

   967 proof (rule up_eqI)

   968   let ?s = "(%i. monom P (coeff P p i) i)"

   969   fix k

   970   from R have RR: "!!i. (if i = k then coeff P p i else \<zero>) \<in> carrier R"

   971     by simp

   972   show "coeff P (\<Oplus>\<^bsub>P\<^esub> i \<in> {..deg R p}. ?s i) k = coeff P p k"

   973   proof (cases "k <= deg R p")

   974     case True

   975     hence "coeff P (\<Oplus>\<^bsub>P\<^esub> i \<in> {..deg R p}. ?s i) k =

   976           coeff P (\<Oplus>\<^bsub>P\<^esub> i \<in> {..k} \<union> {k<..deg R p}. ?s i) k"

   977       by (simp only: ivl_disj_un_one)

   978     also from True

   979     have "... = coeff P (\<Oplus>\<^bsub>P\<^esub> i \<in> {..k}. ?s i) k"

   980       by (simp cong: R.finsum_cong add: R.finsum_Un_disjoint

   981         ivl_disj_int_one order_less_imp_not_eq2 coeff_finsum R RR Pi_def)

   982     also

   983     have "... = coeff P (\<Oplus>\<^bsub>P\<^esub> i \<in> {..<k} \<union> {k}. ?s i) k"

   984       by (simp only: ivl_disj_un_singleton)

   985     also have "... = coeff P p k"

   986       by (simp cong: R.finsum_cong

   987 	add: ivl_disj_int_singleton coeff_finsum deg_aboveD R RR Pi_def)

   988     finally show ?thesis .

   989   next

   990     case False

   991     hence "coeff P (\<Oplus>\<^bsub>P\<^esub> i \<in> {..deg R p}. ?s i) k =

   992           coeff P (\<Oplus>\<^bsub>P\<^esub> i \<in> {..<deg R p} \<union> {deg R p}. ?s i) k"

   993       by (simp only: ivl_disj_un_singleton)

   994     also from False have "... = coeff P p k"

   995       by (simp cong: R.finsum_cong

   996 	add: ivl_disj_int_singleton coeff_finsum deg_aboveD R Pi_def)

   997     finally show ?thesis .

   998   qed

   999 qed (simp_all add: R Pi_def)

  1000

  1001 lemma up_repr_le:

  1002   "[| deg R p <= n; p \<in> carrier P |] ==>

  1003   (\<Oplus>\<^bsub>P\<^esub> i \<in> {..n}. monom P (coeff P p i) i) = p"

  1004 proof -

  1005   let ?s = "(%i. monom P (coeff P p i) i)"

  1006   assume R: "p \<in> carrier P" and "deg R p <= n"

  1007   then have "finsum P ?s {..n} = finsum P ?s ({..deg R p} \<union> {deg R p<..n})"

  1008     by (simp only: ivl_disj_un_one)

  1009   also have "... = finsum P ?s {..deg R p}"

  1010     by (simp cong: P.finsum_cong add: P.finsum_Un_disjoint ivl_disj_int_one

  1011       deg_aboveD R Pi_def)

  1012   also have "... = p" using R by (rule up_repr)

  1013   finally show ?thesis .

  1014 qed

  1015

  1016 end

  1017

  1018

  1019 subsection {* Polynomials over Integral Domains *}

  1020

  1021 lemma domainI:

  1022   assumes cring: "cring R"

  1023     and one_not_zero: "one R ~= zero R"

  1024     and integral: "!!a b. [| mult R a b = zero R; a \<in> carrier R;

  1025       b \<in> carrier R |] ==> a = zero R | b = zero R"

  1026   shows "domain R"

  1027   by (auto intro!: domain.intro domain_axioms.intro cring.axioms assms

  1028     del: disjCI)

  1029

  1030 context UP_domain

  1031 begin

  1032

  1033 lemma UP_one_not_zero:

  1034   "\<one>\<^bsub>P\<^esub> ~= \<zero>\<^bsub>P\<^esub>"

  1035 proof

  1036   assume "\<one>\<^bsub>P\<^esub> = \<zero>\<^bsub>P\<^esub>"

  1037   hence "coeff P \<one>\<^bsub>P\<^esub> 0 = (coeff P \<zero>\<^bsub>P\<^esub> 0)" by simp

  1038   hence "\<one> = \<zero>" by simp

  1039   with R.one_not_zero show "False" by contradiction

  1040 qed

  1041

  1042 lemma UP_integral:

  1043   "[| p \<otimes>\<^bsub>P\<^esub> q = \<zero>\<^bsub>P\<^esub>; p \<in> carrier P; q \<in> carrier P |] ==> p = \<zero>\<^bsub>P\<^esub> | q = \<zero>\<^bsub>P\<^esub>"

  1044 proof -

  1045   fix p q

  1046   assume pq: "p \<otimes>\<^bsub>P\<^esub> q = \<zero>\<^bsub>P\<^esub>" and R: "p \<in> carrier P" "q \<in> carrier P"

  1047   show "p = \<zero>\<^bsub>P\<^esub> | q = \<zero>\<^bsub>P\<^esub>"

  1048   proof (rule classical)

  1049     assume c: "~ (p = \<zero>\<^bsub>P\<^esub> | q = \<zero>\<^bsub>P\<^esub>)"

  1050     with R have "deg R p + deg R q = deg R (p \<otimes>\<^bsub>P\<^esub> q)" by simp

  1051     also from pq have "... = 0" by simp

  1052     finally have "deg R p + deg R q = 0" .

  1053     then have f1: "deg R p = 0 & deg R q = 0" by simp

  1054     from f1 R have "p = (\<Oplus>\<^bsub>P\<^esub> i \<in> {..0}. monom P (coeff P p i) i)"

  1055       by (simp only: up_repr_le)

  1056     also from R have "... = monom P (coeff P p 0) 0" by simp

  1057     finally have p: "p = monom P (coeff P p 0) 0" .

  1058     from f1 R have "q = (\<Oplus>\<^bsub>P\<^esub> i \<in> {..0}. monom P (coeff P q i) i)"

  1059       by (simp only: up_repr_le)

  1060     also from R have "... = monom P (coeff P q 0) 0" by simp

  1061     finally have q: "q = monom P (coeff P q 0) 0" .

  1062     from R have "coeff P p 0 \<otimes> coeff P q 0 = coeff P (p \<otimes>\<^bsub>P\<^esub> q) 0" by simp

  1063     also from pq have "... = \<zero>" by simp

  1064     finally have "coeff P p 0 \<otimes> coeff P q 0 = \<zero>" .

  1065     with R have "coeff P p 0 = \<zero> | coeff P q 0 = \<zero>"

  1066       by (simp add: R.integral_iff)

  1067     with p q show "p = \<zero>\<^bsub>P\<^esub> | q = \<zero>\<^bsub>P\<^esub>" by fastsimp

  1068   qed

  1069 qed

  1070

  1071 theorem UP_domain:

  1072   "domain P"

  1073   by (auto intro!: domainI UP_cring UP_one_not_zero UP_integral del: disjCI)

  1074

  1075 end

  1076

  1077 text {*

  1078   Interpretation of theorems from @{term domain}.

  1079 *}

  1080

  1081 sublocale UP_domain < "domain" P

  1082   by intro_locales (rule domain.axioms UP_domain)+

  1083

  1084

  1085 subsection {* The Evaluation Homomorphism and Universal Property*}

  1086

  1087 (* alternative congruence rule (possibly more efficient)

  1088 lemma (in abelian_monoid) finsum_cong2:

  1089   "[| !!i. i \<in> A ==> f i \<in> carrier G = True; A = B;

  1090   !!i. i \<in> B ==> f i = g i |] ==> finsum G f A = finsum G g B"

  1091   sorry*)

  1092

  1093 lemma (in abelian_monoid) boundD_carrier:

  1094   "[| bound \<zero> n f; n < m |] ==> f m \<in> carrier G"

  1095   by auto

  1096

  1097 context ring

  1098 begin

  1099

  1100 theorem diagonal_sum:

  1101   "[| f \<in> {..n + m::nat} -> carrier R; g \<in> {..n + m} -> carrier R |] ==>

  1102   (\<Oplus>k \<in> {..n + m}. \<Oplus>i \<in> {..k}. f i \<otimes> g (k - i)) =

  1103   (\<Oplus>k \<in> {..n + m}. \<Oplus>i \<in> {..n + m - k}. f k \<otimes> g i)"

  1104 proof -

  1105   assume Rf: "f \<in> {..n + m} -> carrier R" and Rg: "g \<in> {..n + m} -> carrier R"

  1106   {

  1107     fix j

  1108     have "j <= n + m ==>

  1109       (\<Oplus>k \<in> {..j}. \<Oplus>i \<in> {..k}. f i \<otimes> g (k - i)) =

  1110       (\<Oplus>k \<in> {..j}. \<Oplus>i \<in> {..j - k}. f k \<otimes> g i)"

  1111     proof (induct j)

  1112       case 0 from Rf Rg show ?case by (simp add: Pi_def)

  1113     next

  1114       case (Suc j)

  1115       have R6: "!!i k. [| k <= j; i <= Suc j - k |] ==> g i \<in> carrier R"

  1116         using Suc by (auto intro!: funcset_mem [OF Rg])

  1117       have R8: "!!i k. [| k <= Suc j; i <= k |] ==> g (k - i) \<in> carrier R"

  1118         using Suc by (auto intro!: funcset_mem [OF Rg])

  1119       have R9: "!!i k. [| k <= Suc j |] ==> f k \<in> carrier R"

  1120         using Suc by (auto intro!: funcset_mem [OF Rf])

  1121       have R10: "!!i k. [| k <= Suc j; i <= Suc j - k |] ==> g i \<in> carrier R"

  1122         using Suc by (auto intro!: funcset_mem [OF Rg])

  1123       have R11: "g 0 \<in> carrier R"

  1124         using Suc by (auto intro!: funcset_mem [OF Rg])

  1125       from Suc show ?case

  1126         by (simp cong: finsum_cong add: Suc_diff_le a_ac

  1127           Pi_def R6 R8 R9 R10 R11)

  1128     qed

  1129   }

  1130   then show ?thesis by fast

  1131 qed

  1132

  1133 theorem cauchy_product:

  1134   assumes bf: "bound \<zero> n f" and bg: "bound \<zero> m g"

  1135     and Rf: "f \<in> {..n} -> carrier R" and Rg: "g \<in> {..m} -> carrier R"

  1136   shows "(\<Oplus>k \<in> {..n + m}. \<Oplus>i \<in> {..k}. f i \<otimes> g (k - i)) =

  1137     (\<Oplus>i \<in> {..n}. f i) \<otimes> (\<Oplus>i \<in> {..m}. g i)"      (* State reverse direction? *)

  1138 proof -

  1139   have f: "!!x. f x \<in> carrier R"

  1140   proof -

  1141     fix x

  1142     show "f x \<in> carrier R"

  1143       using Rf bf boundD_carrier by (cases "x <= n") (auto simp: Pi_def)

  1144   qed

  1145   have g: "!!x. g x \<in> carrier R"

  1146   proof -

  1147     fix x

  1148     show "g x \<in> carrier R"

  1149       using Rg bg boundD_carrier by (cases "x <= m") (auto simp: Pi_def)

  1150   qed

  1151   from f g have "(\<Oplus>k \<in> {..n + m}. \<Oplus>i \<in> {..k}. f i \<otimes> g (k - i)) =

  1152       (\<Oplus>k \<in> {..n + m}. \<Oplus>i \<in> {..n + m - k}. f k \<otimes> g i)"

  1153     by (simp add: diagonal_sum Pi_def)

  1154   also have "... = (\<Oplus>k \<in> {..n} \<union> {n<..n + m}. \<Oplus>i \<in> {..n + m - k}. f k \<otimes> g i)"

  1155     by (simp only: ivl_disj_un_one)

  1156   also from f g have "... = (\<Oplus>k \<in> {..n}. \<Oplus>i \<in> {..n + m - k}. f k \<otimes> g i)"

  1157     by (simp cong: finsum_cong

  1158       add: bound.bound [OF bf] finsum_Un_disjoint ivl_disj_int_one Pi_def)

  1159   also from f g

  1160   have "... = (\<Oplus>k \<in> {..n}. \<Oplus>i \<in> {..m} \<union> {m<..n + m - k}. f k \<otimes> g i)"

  1161     by (simp cong: finsum_cong add: ivl_disj_un_one le_add_diff Pi_def)

  1162   also from f g have "... = (\<Oplus>k \<in> {..n}. \<Oplus>i \<in> {..m}. f k \<otimes> g i)"

  1163     by (simp cong: finsum_cong

  1164       add: bound.bound [OF bg] finsum_Un_disjoint ivl_disj_int_one Pi_def)

  1165   also from f g have "... = (\<Oplus>i \<in> {..n}. f i) \<otimes> (\<Oplus>i \<in> {..m}. g i)"

  1166     by (simp add: finsum_ldistr diagonal_sum Pi_def,

  1167       simp cong: finsum_cong add: finsum_rdistr Pi_def)

  1168   finally show ?thesis .

  1169 qed

  1170

  1171 end

  1172

  1173 lemma (in UP_ring) const_ring_hom:

  1174   "(%a. monom P a 0) \<in> ring_hom R P"

  1175   by (auto intro!: ring_hom_memI intro: up_eqI simp: monom_mult_is_smult)

  1176

  1177 definition

  1178   eval :: "[('a, 'm) ring_scheme, ('b, 'n) ring_scheme,

  1179            'a => 'b, 'b, nat => 'a] => 'b"

  1180   where "eval R S phi s == \<lambda>p \<in> carrier (UP R).

  1181     \<Oplus>\<^bsub>S\<^esub>i \<in> {..deg R p}. phi (coeff (UP R) p i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i"

  1182

  1183 context UP

  1184 begin

  1185

  1186 lemma eval_on_carrier:

  1187   fixes S (structure)

  1188   shows "p \<in> carrier P ==>

  1189   eval R S phi s p = (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R p}. phi (coeff P p i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1190   by (unfold eval_def, fold P_def) simp

  1191

  1192 lemma eval_extensional:

  1193   "eval R S phi p \<in> extensional (carrier P)"

  1194   by (unfold eval_def, fold P_def) simp

  1195

  1196 end

  1197

  1198 text {* The universal property of the polynomial ring *}

  1199

  1200 locale UP_pre_univ_prop = ring_hom_cring + UP_cring

  1201

  1202 (* FIXME print_locale ring_hom_cring fails *)

  1203

  1204 locale UP_univ_prop = UP_pre_univ_prop +

  1205   fixes s and Eval

  1206   assumes indet_img_carrier [simp, intro]: "s \<in> carrier S"

  1207   defines Eval_def: "Eval == eval R S h s"

  1208

  1209 text{*JE: I have moved the following lemma from Ring.thy and lifted then to the locale @{term ring_hom_ring} from @{term ring_hom_cring}.*}

  1210 text{*JE: I was considering using it in @{text eval_ring_hom}, but that property does not hold for non commutative rings, so

  1211   maybe it is not that necessary.*}

  1212

  1213 lemma (in ring_hom_ring) hom_finsum [simp]:

  1214   "[| finite A; f \<in> A -> carrier R |] ==>

  1215   h (finsum R f A) = finsum S (h o f) A"

  1216 proof (induct set: finite)

  1217   case empty then show ?case by simp

  1218 next

  1219   case insert then show ?case by (simp add: Pi_def)

  1220 qed

  1221

  1222 context UP_pre_univ_prop

  1223 begin

  1224

  1225 theorem eval_ring_hom:

  1226   assumes S: "s \<in> carrier S"

  1227   shows "eval R S h s \<in> ring_hom P S"

  1228 proof (rule ring_hom_memI)

  1229   fix p

  1230   assume R: "p \<in> carrier P"

  1231   then show "eval R S h s p \<in> carrier S"

  1232     by (simp only: eval_on_carrier) (simp add: S Pi_def)

  1233 next

  1234   fix p q

  1235   assume R: "p \<in> carrier P" "q \<in> carrier P"

  1236   then show "eval R S h s (p \<oplus>\<^bsub>P\<^esub> q) = eval R S h s p \<oplus>\<^bsub>S\<^esub> eval R S h s q"

  1237   proof (simp only: eval_on_carrier P.a_closed)

  1238     from S R have

  1239       "(\<Oplus>\<^bsub>S \<^esub>i\<in>{..deg R (p \<oplus>\<^bsub>P\<^esub> q)}. h (coeff P (p \<oplus>\<^bsub>P\<^esub> q) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) =

  1240       (\<Oplus>\<^bsub>S \<^esub>i\<in>{..deg R (p \<oplus>\<^bsub>P\<^esub> q)} \<union> {deg R (p \<oplus>\<^bsub>P\<^esub> q)<..max (deg R p) (deg R q)}.

  1241         h (coeff P (p \<oplus>\<^bsub>P\<^esub> q) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1242       by (simp cong: S.finsum_cong

  1243         add: deg_aboveD S.finsum_Un_disjoint ivl_disj_int_one Pi_def del: coeff_add)

  1244     also from R have "... =

  1245         (\<Oplus>\<^bsub>S\<^esub> i \<in> {..max (deg R p) (deg R q)}.

  1246           h (coeff P (p \<oplus>\<^bsub>P\<^esub> q) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1247       by (simp add: ivl_disj_un_one)

  1248     also from R S have "... =

  1249       (\<Oplus>\<^bsub>S\<^esub>i\<in>{..max (deg R p) (deg R q)}. h (coeff P p i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) \<oplus>\<^bsub>S\<^esub>

  1250       (\<Oplus>\<^bsub>S\<^esub>i\<in>{..max (deg R p) (deg R q)}. h (coeff P q i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1251       by (simp cong: S.finsum_cong

  1252         add: S.l_distr deg_aboveD ivl_disj_int_one Pi_def)

  1253     also have "... =

  1254         (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R p} \<union> {deg R p<..max (deg R p) (deg R q)}.

  1255           h (coeff P p i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) \<oplus>\<^bsub>S\<^esub>

  1256         (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R q} \<union> {deg R q<..max (deg R p) (deg R q)}.

  1257           h (coeff P q i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1258       by (simp only: ivl_disj_un_one le_maxI1 le_maxI2)

  1259     also from R S have "... =

  1260       (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R p}. h (coeff P p i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) \<oplus>\<^bsub>S\<^esub>

  1261       (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R q}. h (coeff P q i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1262       by (simp cong: S.finsum_cong

  1263         add: deg_aboveD S.finsum_Un_disjoint ivl_disj_int_one Pi_def)

  1264     finally show

  1265       "(\<Oplus>\<^bsub>S\<^esub>i \<in> {..deg R (p \<oplus>\<^bsub>P\<^esub> q)}. h (coeff P (p \<oplus>\<^bsub>P\<^esub> q) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) =

  1266       (\<Oplus>\<^bsub>S\<^esub>i \<in> {..deg R p}. h (coeff P p i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) \<oplus>\<^bsub>S\<^esub>

  1267       (\<Oplus>\<^bsub>S\<^esub>i \<in> {..deg R q}. h (coeff P q i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)" .

  1268   qed

  1269 next

  1270   show "eval R S h s \<one>\<^bsub>P\<^esub> = \<one>\<^bsub>S\<^esub>"

  1271     by (simp only: eval_on_carrier UP_one_closed) simp

  1272 next

  1273   fix p q

  1274   assume R: "p \<in> carrier P" "q \<in> carrier P"

  1275   then show "eval R S h s (p \<otimes>\<^bsub>P\<^esub> q) = eval R S h s p \<otimes>\<^bsub>S\<^esub> eval R S h s q"

  1276   proof (simp only: eval_on_carrier UP_mult_closed)

  1277     from R S have

  1278       "(\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R (p \<otimes>\<^bsub>P\<^esub> q)}. h (coeff P (p \<otimes>\<^bsub>P\<^esub> q) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) =

  1279       (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R (p \<otimes>\<^bsub>P\<^esub> q)} \<union> {deg R (p \<otimes>\<^bsub>P\<^esub> q)<..deg R p + deg R q}.

  1280         h (coeff P (p \<otimes>\<^bsub>P\<^esub> q) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1281       by (simp cong: S.finsum_cong

  1282         add: deg_aboveD S.finsum_Un_disjoint ivl_disj_int_one Pi_def

  1283         del: coeff_mult)

  1284     also from R have "... =

  1285       (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R p + deg R q}. h (coeff P (p \<otimes>\<^bsub>P\<^esub> q) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1286       by (simp only: ivl_disj_un_one deg_mult_ring)

  1287     also from R S have "... =

  1288       (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R p + deg R q}.

  1289          \<Oplus>\<^bsub>S\<^esub> k \<in> {..i}.

  1290            h (coeff P p k) \<otimes>\<^bsub>S\<^esub> h (coeff P q (i - k)) \<otimes>\<^bsub>S\<^esub>

  1291            (s (^)\<^bsub>S\<^esub> k \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> (i - k)))"

  1292       by (simp cong: S.finsum_cong add: S.nat_pow_mult Pi_def

  1293         S.m_ac S.finsum_rdistr)

  1294     also from R S have "... =

  1295       (\<Oplus>\<^bsub>S\<^esub> i\<in>{..deg R p}. h (coeff P p i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) \<otimes>\<^bsub>S\<^esub>

  1296       (\<Oplus>\<^bsub>S\<^esub> i\<in>{..deg R q}. h (coeff P q i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1297       by (simp add: S.cauchy_product [THEN sym] bound.intro deg_aboveD S.m_ac

  1298         Pi_def)

  1299     finally show

  1300       "(\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R (p \<otimes>\<^bsub>P\<^esub> q)}. h (coeff P (p \<otimes>\<^bsub>P\<^esub> q) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) =

  1301       (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R p}. h (coeff P p i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) \<otimes>\<^bsub>S\<^esub>

  1302       (\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R q}. h (coeff P q i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)" .

  1303   qed

  1304 qed

  1305

  1306 text {*

  1307   The following lemma could be proved in @{text UP_cring} with the additional

  1308   assumption that @{text h} is closed. *}

  1309

  1310 lemma (in UP_pre_univ_prop) eval_const:

  1311   "[| s \<in> carrier S; r \<in> carrier R |] ==> eval R S h s (monom P r 0) = h r"

  1312   by (simp only: eval_on_carrier monom_closed) simp

  1313

  1314 text {* Further properties of the evaluation homomorphism. *}

  1315

  1316 text {* The following proof is complicated by the fact that in arbitrary

  1317   rings one might have @{term "one R = zero R"}. *}

  1318

  1319 (* TODO: simplify by cases "one R = zero R" *)

  1320

  1321 lemma (in UP_pre_univ_prop) eval_monom1:

  1322   assumes S: "s \<in> carrier S"

  1323   shows "eval R S h s (monom P \<one> 1) = s"

  1324 proof (simp only: eval_on_carrier monom_closed R.one_closed)

  1325    from S have

  1326     "(\<Oplus>\<^bsub>S\<^esub> i\<in>{..deg R (monom P \<one> 1)}. h (coeff P (monom P \<one> 1) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) =

  1327     (\<Oplus>\<^bsub>S\<^esub> i\<in>{..deg R (monom P \<one> 1)} \<union> {deg R (monom P \<one> 1)<..1}.

  1328       h (coeff P (monom P \<one> 1) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1329     by (simp cong: S.finsum_cong del: coeff_monom

  1330       add: deg_aboveD S.finsum_Un_disjoint ivl_disj_int_one Pi_def)

  1331   also have "... =

  1332     (\<Oplus>\<^bsub>S\<^esub> i \<in> {..1}. h (coeff P (monom P \<one> 1) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i)"

  1333     by (simp only: ivl_disj_un_one deg_monom_le R.one_closed)

  1334   also have "... = s"

  1335   proof (cases "s = \<zero>\<^bsub>S\<^esub>")

  1336     case True then show ?thesis by (simp add: Pi_def)

  1337   next

  1338     case False then show ?thesis by (simp add: S Pi_def)

  1339   qed

  1340   finally show "(\<Oplus>\<^bsub>S\<^esub> i \<in> {..deg R (monom P \<one> 1)}.

  1341     h (coeff P (monom P \<one> 1) i) \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> i) = s" .

  1342 qed

  1343

  1344 end

  1345

  1346 text {* Interpretation of ring homomorphism lemmas. *}

  1347

  1348 sublocale UP_univ_prop < ring_hom_cring P S Eval

  1349   apply (unfold Eval_def)

  1350   apply intro_locales

  1351   apply (rule ring_hom_cring.axioms)

  1352   apply (rule ring_hom_cring.intro)

  1353   apply unfold_locales

  1354   apply (rule eval_ring_hom)

  1355   apply rule

  1356   done

  1357

  1358 lemma (in UP_cring) monom_pow:

  1359   assumes R: "a \<in> carrier R"

  1360   shows "(monom P a n) (^)\<^bsub>P\<^esub> m = monom P (a (^) m) (n * m)"

  1361 proof (induct m)

  1362   case 0 from R show ?case by simp

  1363 next

  1364   case Suc with R show ?case

  1365     by (simp del: monom_mult add: monom_mult [THEN sym] add_commute)

  1366 qed

  1367

  1368 lemma (in ring_hom_cring) hom_pow [simp]:

  1369   "x \<in> carrier R ==> h (x (^) n) = h x (^)\<^bsub>S\<^esub> (n::nat)"

  1370   by (induct n) simp_all

  1371

  1372 lemma (in UP_univ_prop) Eval_monom:

  1373   "r \<in> carrier R ==> Eval (monom P r n) = h r \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> n"

  1374 proof -

  1375   assume R: "r \<in> carrier R"

  1376   from R have "Eval (monom P r n) = Eval (monom P r 0 \<otimes>\<^bsub>P\<^esub> (monom P \<one> 1) (^)\<^bsub>P\<^esub> n)"

  1377     by (simp del: monom_mult add: monom_mult [THEN sym] monom_pow)

  1378   also

  1379   from R eval_monom1 [where s = s, folded Eval_def]

  1380   have "... = h r \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> n"

  1381     by (simp add: eval_const [where s = s, folded Eval_def])

  1382   finally show ?thesis .

  1383 qed

  1384

  1385 lemma (in UP_pre_univ_prop) eval_monom:

  1386   assumes R: "r \<in> carrier R" and S: "s \<in> carrier S"

  1387   shows "eval R S h s (monom P r n) = h r \<otimes>\<^bsub>S\<^esub> s (^)\<^bsub>S\<^esub> n"

  1388 proof -

  1389   interpret UP_univ_prop R S h P s "eval R S h s"

  1390     using UP_pre_univ_prop_axioms P_def R S

  1391     by (auto intro: UP_univ_prop.intro UP_univ_prop_axioms.intro)

  1392   from R

  1393   show ?thesis by (rule Eval_monom)

  1394 qed

  1395

  1396 lemma (in UP_univ_prop) Eval_smult:

  1397   "[| r \<in> carrier R; p \<in> carrier P |] ==> Eval (r \<odot>\<^bsub>P\<^esub> p) = h r \<otimes>\<^bsub>S\<^esub> Eval p"

  1398 proof -

  1399   assume R: "r \<in> carrier R" and P: "p \<in> carrier P"

  1400   then show ?thesis

  1401     by (simp add: monom_mult_is_smult [THEN sym]

  1402       eval_const [where s = s, folded Eval_def])

  1403 qed

  1404

  1405 lemma ring_hom_cringI:

  1406   assumes "cring R"

  1407     and "cring S"

  1408     and "h \<in> ring_hom R S"

  1409   shows "ring_hom_cring R S h"

  1410   by (fast intro: ring_hom_cring.intro ring_hom_cring_axioms.intro

  1411     cring.axioms assms)

  1412

  1413 context UP_pre_univ_prop

  1414 begin

  1415

  1416 lemma UP_hom_unique:

  1417   assumes "ring_hom_cring P S Phi"

  1418   assumes Phi: "Phi (monom P \<one> (Suc 0)) = s"

  1419       "!!r. r \<in> carrier R ==> Phi (monom P r 0) = h r"

  1420   assumes "ring_hom_cring P S Psi"

  1421   assumes Psi: "Psi (monom P \<one> (Suc 0)) = s"

  1422       "!!r. r \<in> carrier R ==> Psi (monom P r 0) = h r"

  1423     and P: "p \<in> carrier P" and S: "s \<in> carrier S"

  1424   shows "Phi p = Psi p"

  1425 proof -

  1426   interpret ring_hom_cring P S Phi by fact

  1427   interpret ring_hom_cring P S Psi by fact

  1428   have "Phi p =

  1429       Phi (\<Oplus>\<^bsub>P \<^esub>i \<in> {..deg R p}. monom P (coeff P p i) 0 \<otimes>\<^bsub>P\<^esub> monom P \<one> 1 (^)\<^bsub>P\<^esub> i)"

  1430     by (simp add: up_repr P monom_mult [THEN sym] monom_pow del: monom_mult)

  1431   also

  1432   have "... =

  1433       Psi (\<Oplus>\<^bsub>P \<^esub>i\<in>{..deg R p}. monom P (coeff P p i) 0 \<otimes>\<^bsub>P\<^esub> monom P \<one> 1 (^)\<^bsub>P\<^esub> i)"

  1434     by (simp add: Phi Psi P Pi_def comp_def)

  1435   also have "... = Psi p"

  1436     by (simp add: up_repr P monom_mult [THEN sym] monom_pow del: monom_mult)

  1437   finally show ?thesis .

  1438 qed

  1439

  1440 lemma ring_homD:

  1441   assumes Phi: "Phi \<in> ring_hom P S"

  1442   shows "ring_hom_cring P S Phi"

  1443 proof (rule ring_hom_cring.intro)

  1444   show "ring_hom_cring_axioms P S Phi"

  1445   by (rule ring_hom_cring_axioms.intro) (rule Phi)

  1446 qed unfold_locales

  1447

  1448 theorem UP_universal_property:

  1449   assumes S: "s \<in> carrier S"

  1450   shows "EX! Phi. Phi \<in> ring_hom P S \<inter> extensional (carrier P) &

  1451     Phi (monom P \<one> 1) = s &

  1452     (ALL r : carrier R. Phi (monom P r 0) = h r)"

  1453   using S eval_monom1

  1454   apply (auto intro: eval_ring_hom eval_const eval_extensional)

  1455   apply (rule extensionalityI)

  1456   apply (auto intro: UP_hom_unique ring_homD)

  1457   done

  1458

  1459 end

  1460

  1461 text{*JE: The following lemma was added by me; it might be even lifted to a simpler locale*}

  1462

  1463 context monoid

  1464 begin

  1465

  1466 lemma nat_pow_eone[simp]: assumes x_in_G: "x \<in> carrier G" shows "x (^) (1::nat) = x"

  1467   using nat_pow_Suc [of x 0] unfolding nat_pow_0 [of x] unfolding l_one [OF x_in_G] by simp

  1468

  1469 end

  1470

  1471 context UP_ring

  1472 begin

  1473

  1474 abbreviation lcoeff :: "(nat =>'a) => 'a" where "lcoeff p == coeff P p (deg R p)"

  1475

  1476 lemma lcoeff_nonzero2: assumes p_in_R: "p \<in> carrier P" and p_not_zero: "p \<noteq> \<zero>\<^bsub>P\<^esub>" shows "lcoeff p \<noteq> \<zero>"

  1477   using lcoeff_nonzero [OF p_not_zero p_in_R] .

  1478

  1479 subsection{*The long division algorithm: some previous facts.*}

  1480

  1481 lemma coeff_minus [simp]:

  1482   assumes p: "p \<in> carrier P" and q: "q \<in> carrier P" shows "coeff P (p \<ominus>\<^bsub>P\<^esub> q) n = coeff P p n \<ominus> coeff P q n"

  1483   unfolding a_minus_def [OF p q] unfolding coeff_add [OF p a_inv_closed [OF q]] unfolding coeff_a_inv [OF q]

  1484   using coeff_closed [OF p, of n] using coeff_closed [OF q, of n] by algebra

  1485

  1486 lemma lcoeff_closed [simp]: assumes p: "p \<in> carrier P" shows "lcoeff p \<in> carrier R"

  1487   using coeff_closed [OF p, of "deg R p"] by simp

  1488

  1489 lemma deg_smult_decr: assumes a_in_R: "a \<in> carrier R" and f_in_P: "f \<in> carrier P" shows "deg R (a \<odot>\<^bsub>P\<^esub> f) \<le> deg R f"

  1490   using deg_smult_ring [OF a_in_R f_in_P] by (cases "a = \<zero>", auto)

  1491

  1492 lemma coeff_monom_mult: assumes R: "c \<in> carrier R" and P: "p \<in> carrier P"

  1493   shows "coeff P (monom P c n \<otimes>\<^bsub>P\<^esub> p) (m + n) = c \<otimes> (coeff P p m)"

  1494 proof -

  1495   have "coeff P (monom P c n \<otimes>\<^bsub>P\<^esub> p) (m + n) = (\<Oplus>i\<in>{..m + n}. (if n = i then c else \<zero>) \<otimes> coeff P p (m + n - i))"

  1496     unfolding coeff_mult [OF monom_closed [OF R, of n] P, of "m + n"] unfolding coeff_monom [OF R, of n] by simp

  1497   also have "(\<Oplus>i\<in>{..m + n}. (if n = i then c else \<zero>) \<otimes> coeff P p (m + n - i)) =

  1498     (\<Oplus>i\<in>{..m + n}. (if n = i then c \<otimes> coeff P p (m + n - i) else \<zero>))"

  1499     using  R.finsum_cong [of "{..m + n}" "{..m + n}" "(\<lambda>i::nat. (if n = i then c else \<zero>) \<otimes> coeff P p (m + n - i))"

  1500       "(\<lambda>i::nat. (if n = i then c \<otimes> coeff P p (m + n - i) else \<zero>))"]

  1501     using coeff_closed [OF P] unfolding Pi_def simp_implies_def using R by auto

  1502   also have "\<dots> = c \<otimes> coeff P p m" using R.finsum_singleton [of n "{..m + n}" "(\<lambda>i. c \<otimes> coeff P p (m + n - i))"]

  1503     unfolding Pi_def using coeff_closed [OF P] using P R by auto

  1504   finally show ?thesis by simp

  1505 qed

  1506

  1507 lemma deg_lcoeff_cancel:

  1508   assumes p_in_P: "p \<in> carrier P" and q_in_P: "q \<in> carrier P" and r_in_P: "r \<in> carrier P"

  1509   and deg_r_nonzero: "deg R r \<noteq> 0"

  1510   and deg_R_p: "deg R p \<le> deg R r" and deg_R_q: "deg R q \<le> deg R r"

  1511   and coeff_R_p_eq_q: "coeff P p (deg R r) = \<ominus>\<^bsub>R\<^esub> (coeff P q (deg R r))"

  1512   shows "deg R (p \<oplus>\<^bsub>P\<^esub> q) < deg R r"

  1513 proof -

  1514   have deg_le: "deg R (p \<oplus>\<^bsub>P\<^esub> q) \<le> deg R r"

  1515   proof (rule deg_aboveI)

  1516     fix m

  1517     assume deg_r_le: "deg R r < m"

  1518     show "coeff P (p \<oplus>\<^bsub>P\<^esub> q) m = \<zero>"

  1519     proof -

  1520       have slp: "deg R p < m" and "deg R q < m" using deg_R_p deg_R_q using deg_r_le by auto

  1521       then have max_sl: "max (deg R p) (deg R q) < m" by simp

  1522       then have "deg R (p \<oplus>\<^bsub>P\<^esub> q) < m" using deg_add [OF p_in_P q_in_P] by arith

  1523       with deg_R_p deg_R_q show ?thesis using coeff_add [OF p_in_P q_in_P, of m]

  1524 	using deg_aboveD [of "p \<oplus>\<^bsub>P\<^esub> q" m] using p_in_P q_in_P by simp

  1525     qed

  1526   qed (simp add: p_in_P q_in_P)

  1527   moreover have deg_ne: "deg R (p \<oplus>\<^bsub>P\<^esub> q) \<noteq> deg R r"

  1528   proof (rule ccontr)

  1529     assume nz: "\<not> deg R (p \<oplus>\<^bsub>P\<^esub> q) \<noteq> deg R r" then have deg_eq: "deg R (p \<oplus>\<^bsub>P\<^esub> q) = deg R r" by simp

  1530     from deg_r_nonzero have r_nonzero: "r \<noteq> \<zero>\<^bsub>P\<^esub>" by (cases "r = \<zero>\<^bsub>P\<^esub>", simp_all)

  1531     have "coeff P (p \<oplus>\<^bsub>P\<^esub> q) (deg R r) = \<zero>\<^bsub>R\<^esub>" using coeff_add [OF p_in_P q_in_P, of "deg R r"] using coeff_R_p_eq_q

  1532       using coeff_closed [OF p_in_P, of "deg R r"] coeff_closed [OF q_in_P, of "deg R r"] by algebra

  1533     with lcoeff_nonzero [OF r_nonzero r_in_P]  and deg_eq show False using lcoeff_nonzero [of "p \<oplus>\<^bsub>P\<^esub> q"] using p_in_P q_in_P

  1534       using deg_r_nonzero by (cases "p \<oplus>\<^bsub>P\<^esub> q \<noteq> \<zero>\<^bsub>P\<^esub>", auto)

  1535   qed

  1536   ultimately show ?thesis by simp

  1537 qed

  1538

  1539 lemma monom_deg_mult:

  1540   assumes f_in_P: "f \<in> carrier P" and g_in_P: "g \<in> carrier P" and deg_le: "deg R g \<le> deg R f"

  1541   and a_in_R: "a \<in> carrier R"

  1542   shows "deg R (g \<otimes>\<^bsub>P\<^esub> monom P a (deg R f - deg R g)) \<le> deg R f"

  1543   using deg_mult_ring [OF g_in_P monom_closed [OF a_in_R, of "deg R f - deg R g"]]

  1544   apply (cases "a = \<zero>") using g_in_P apply simp

  1545   using deg_monom [OF _ a_in_R, of "deg R f - deg R g"] using deg_le by simp

  1546

  1547 lemma deg_zero_impl_monom:

  1548   assumes f_in_P: "f \<in> carrier P" and deg_f: "deg R f = 0"

  1549   shows "f = monom P (coeff P f 0) 0"

  1550   apply (rule up_eqI) using coeff_monom [OF coeff_closed [OF f_in_P], of 0 0]

  1551   using f_in_P deg_f using deg_aboveD [of f _] by auto

  1552

  1553 end

  1554

  1555

  1556 subsection {* The long division proof for commutative rings *}

  1557

  1558 context UP_cring

  1559 begin

  1560

  1561 lemma exI3: assumes exist: "Pred x y z"

  1562   shows "\<exists> x y z. Pred x y z"

  1563   using exist by blast

  1564

  1565 text {* Jacobson's Theorem 2.14 *}

  1566

  1567 lemma long_div_theorem:

  1568   assumes g_in_P [simp]: "g \<in> carrier P" and f_in_P [simp]: "f \<in> carrier P"

  1569   and g_not_zero: "g \<noteq> \<zero>\<^bsub>P\<^esub>"

  1570   shows "\<exists> q r (k::nat). (q \<in> carrier P) \<and> (r \<in> carrier P) \<and> (lcoeff g)(^)\<^bsub>R\<^esub>k \<odot>\<^bsub>P\<^esub> f = g \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r \<and> (r = \<zero>\<^bsub>P\<^esub> | deg R r < deg R g)"

  1571 proof -

  1572   let ?pred = "(\<lambda> q r (k::nat).

  1573     (q \<in> carrier P) \<and> (r \<in> carrier P) \<and> (lcoeff g)(^)\<^bsub>R\<^esub>k \<odot>\<^bsub>P\<^esub> f = g \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r \<and> (r = \<zero>\<^bsub>P\<^esub> | deg R r < deg R g))"

  1574     and ?lg = "lcoeff g"

  1575   show ?thesis

  1576     (*JE: we distinguish some particular cases where the solution is almost direct.*)

  1577   proof (cases "deg R f < deg R g")

  1578     case True

  1579       (*JE: if the degree of f is smaller than the one of g the solution is straightforward.*)

  1580       (* CB: avoid exI3 *)

  1581       have "?pred \<zero>\<^bsub>P\<^esub> f 0" using True by force

  1582       then show ?thesis by fast

  1583   next

  1584     case False then have deg_g_le_deg_f: "deg R g \<le> deg R f" by simp

  1585     {

  1586       (*JE: we now apply the induction hypothesis with some additional facts required*)

  1587       from f_in_P deg_g_le_deg_f show ?thesis

  1588       proof (induct n \<equiv> "deg R f" arbitrary: "f" rule: nat_less_induct)

  1589 	fix n f

  1590 	assume hypo: "\<forall>m<n. \<forall>x. x \<in> carrier P \<longrightarrow>

  1591           deg R g \<le> deg R x \<longrightarrow>

  1592 	  m = deg R x \<longrightarrow>

  1593 	  (\<exists>q r (k::nat). q \<in> carrier P \<and> r \<in> carrier P \<and> lcoeff g (^) k \<odot>\<^bsub>P\<^esub> x = g \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r & (r = \<zero>\<^bsub>P\<^esub> | deg R r < deg R g))"

  1594 	  and prem: "n = deg R f" and f_in_P [simp]: "f \<in> carrier P"

  1595 	  and deg_g_le_deg_f: "deg R g \<le> deg R f"

  1596 	let ?k = "1::nat" and ?r = "(g \<otimes>\<^bsub>P\<^esub> (monom P (lcoeff f) (deg R f - deg R g))) \<oplus>\<^bsub>P\<^esub> \<ominus>\<^bsub>P\<^esub> (lcoeff g \<odot>\<^bsub>P\<^esub> f)"

  1597 	  and ?q = "monom P (lcoeff f) (deg R f - deg R g)"

  1598 	show "\<exists> q r (k::nat). q \<in> carrier P \<and> r \<in> carrier P \<and> lcoeff g (^) k \<odot>\<^bsub>P\<^esub> f = g \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r & (r = \<zero>\<^bsub>P\<^esub> | deg R r < deg R g)"

  1599 	proof -

  1600 	  (*JE: we first extablish the existence of a triple satisfying the previous equation.

  1601 	    Then we will have to prove the second part of the predicate.*)

  1602 	  have exist: "lcoeff g (^) ?k \<odot>\<^bsub>P\<^esub> f = g \<otimes>\<^bsub>P\<^esub> ?q \<oplus>\<^bsub>P\<^esub> \<ominus>\<^bsub>P\<^esub> ?r"

  1603 	    using minus_add

  1604 	    using sym [OF a_assoc [of "g \<otimes>\<^bsub>P\<^esub> ?q" "\<ominus>\<^bsub>P\<^esub> (g \<otimes>\<^bsub>P\<^esub> ?q)" "lcoeff g \<odot>\<^bsub>P\<^esub> f"]]

  1605 	    using r_neg by auto

  1606 	  show ?thesis

  1607 	  proof (cases "deg R (\<ominus>\<^bsub>P\<^esub> ?r) < deg R g")

  1608 	    (*JE: if the degree of the remainder satisfies the statement property we are done*)

  1609 	    case True

  1610 	    {

  1611 	      show ?thesis

  1612 	      proof (rule exI3 [of _ ?q "\<ominus>\<^bsub>P\<^esub> ?r" ?k], intro conjI)

  1613 		show "lcoeff g (^) ?k \<odot>\<^bsub>P\<^esub> f = g \<otimes>\<^bsub>P\<^esub> ?q \<oplus>\<^bsub>P\<^esub> \<ominus>\<^bsub>P\<^esub> ?r" using exist by simp

  1614 		show "\<ominus>\<^bsub>P\<^esub> ?r = \<zero>\<^bsub>P\<^esub> \<or> deg R (\<ominus>\<^bsub>P\<^esub> ?r) < deg R g" using True by simp

  1615 	      qed (simp_all)

  1616 	    }

  1617 	  next

  1618 	    case False note n_deg_r_l_deg_g = False

  1619 	    {

  1620 	      (*JE: otherwise, we verify the conditions of the induction hypothesis.*)

  1621 	      show ?thesis

  1622 	      proof (cases "deg R f = 0")

  1623 		(*JE: the solutions are different if the degree of f is zero or not*)

  1624 		case True

  1625 		{

  1626 		  have deg_g: "deg R g = 0" using True using deg_g_le_deg_f by simp

  1627 		  have "lcoeff g (^) (1::nat) \<odot>\<^bsub>P\<^esub> f = g \<otimes>\<^bsub>P\<^esub> f \<oplus>\<^bsub>P\<^esub> \<zero>\<^bsub>P\<^esub>"

  1628 		    unfolding deg_g apply simp

  1629 		    unfolding sym [OF monom_mult_is_smult [OF coeff_closed [OF g_in_P, of 0] f_in_P]]

  1630 		    using deg_zero_impl_monom [OF g_in_P deg_g] by simp

  1631 		  then show ?thesis using f_in_P by blast

  1632 		}

  1633 	      next

  1634 		case False note deg_f_nzero = False

  1635 		{

  1636 		  (*JE: now it only remains the case where the induction hypothesis can be used.*)

  1637 		  (*JE: we first prove that the degree of the remainder is smaller than the one of f*)

  1638 		  have deg_remainder_l_f: "deg R (\<ominus>\<^bsub>P\<^esub> ?r) < n"

  1639 		  proof -

  1640 		    have "deg R (\<ominus>\<^bsub>P\<^esub> ?r) = deg R ?r" using deg_uminus [of ?r] by simp

  1641 		    also have "\<dots> < deg R f"

  1642 		    proof (rule deg_lcoeff_cancel)

  1643 		      show "deg R (\<ominus>\<^bsub>P\<^esub> (lcoeff g \<odot>\<^bsub>P\<^esub> f)) \<le> deg R f"

  1644 			using deg_smult_ring [of "lcoeff g" f] using prem

  1645 			using lcoeff_nonzero2 [OF g_in_P g_not_zero] by simp

  1646 		      show "deg R (g \<otimes>\<^bsub>P\<^esub> ?q) \<le> deg R f"

  1647 			using monom_deg_mult [OF _ g_in_P, of f "lcoeff f"] and deg_g_le_deg_f

  1648 			by simp

  1649 		      show "coeff P (g \<otimes>\<^bsub>P\<^esub> ?q) (deg R f) = \<ominus> coeff P (\<ominus>\<^bsub>P\<^esub> (lcoeff g \<odot>\<^bsub>P\<^esub> f)) (deg R f)"

  1650 			unfolding coeff_mult [OF g_in_P monom_closed [OF lcoeff_closed [OF f_in_P], of "deg R f - deg R g"], of "deg R f"]

  1651 			unfolding coeff_monom [OF lcoeff_closed [OF f_in_P], of "(deg R f - deg R g)"]

  1652 			using R.finsum_cong' [of "{..deg R f}" "{..deg R f}"

  1653 			  "(\<lambda>i. coeff P g i \<otimes> (if deg R f - deg R g = deg R f - i then lcoeff f else \<zero>))"

  1654 			  "(\<lambda>i. if deg R g = i then coeff P g i \<otimes> lcoeff f else \<zero>)"]

  1655 			using R.finsum_singleton [of "deg R g" "{.. deg R f}" "(\<lambda>i. coeff P g i \<otimes> lcoeff f)"]

  1656 			unfolding Pi_def using deg_g_le_deg_f by force

  1657 		    qed (simp_all add: deg_f_nzero)

  1658 		    finally show "deg R (\<ominus>\<^bsub>P\<^esub> ?r) < n" unfolding prem .

  1659 		  qed

  1660 		  moreover have "\<ominus>\<^bsub>P\<^esub> ?r \<in> carrier P" by simp

  1661 		  moreover obtain m where deg_rem_eq_m: "deg R (\<ominus>\<^bsub>P\<^esub> ?r) = m" by auto

  1662 		  moreover have "deg R g \<le> deg R (\<ominus>\<^bsub>P\<^esub> ?r)" using n_deg_r_l_deg_g by simp

  1663 		    (*JE: now, by applying the induction hypothesis, we obtain new quotient, remainder and exponent.*)

  1664 		  ultimately obtain q' r' k'

  1665 		    where rem_desc: "lcoeff g (^) (k'::nat) \<odot>\<^bsub>P\<^esub> (\<ominus>\<^bsub>P\<^esub> ?r) = g \<otimes>\<^bsub>P\<^esub> q' \<oplus>\<^bsub>P\<^esub> r'"and rem_deg: "(r' = \<zero>\<^bsub>P\<^esub> \<or> deg R r' < deg R g)"

  1666 		    and q'_in_carrier: "q' \<in> carrier P" and r'_in_carrier: "r' \<in> carrier P"

  1667 		    using hypo by blast

  1668 		      (*JE: we now prove that the new quotient, remainder and exponent can be used to get

  1669 		      the quotient, remainder and exponent of the long division theorem*)

  1670 		  show ?thesis

  1671 		  proof (rule exI3 [of _ "((lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> ?q \<oplus>\<^bsub>P\<^esub> q')" r' "Suc k'"], intro conjI)

  1672 		    show "(lcoeff g (^) (Suc k')) \<odot>\<^bsub>P\<^esub> f = g \<otimes>\<^bsub>P\<^esub> ((lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> ?q \<oplus>\<^bsub>P\<^esub> q') \<oplus>\<^bsub>P\<^esub> r'"

  1673 		    proof -

  1674 		      have "(lcoeff g (^) (Suc k')) \<odot>\<^bsub>P\<^esub> f = (lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> (g \<otimes>\<^bsub>P\<^esub> ?q \<oplus>\<^bsub>P\<^esub> \<ominus>\<^bsub>P\<^esub> ?r)"

  1675 			using smult_assoc1 exist by simp

  1676 		      also have "\<dots> = (lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> (g \<otimes>\<^bsub>P\<^esub> ?q) \<oplus>\<^bsub>P\<^esub> ((lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> ( \<ominus>\<^bsub>P\<^esub> ?r))"

  1677 			using UP_smult_r_distr by simp

  1678 		      also have "\<dots> = (lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> (g \<otimes>\<^bsub>P\<^esub> ?q) \<oplus>\<^bsub>P\<^esub> (g \<otimes>\<^bsub>P\<^esub> q' \<oplus>\<^bsub>P\<^esub> r')"

  1679 			using rem_desc by simp

  1680 		      also have "\<dots> = (lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> (g \<otimes>\<^bsub>P\<^esub> ?q) \<oplus>\<^bsub>P\<^esub> g \<otimes>\<^bsub>P\<^esub> q' \<oplus>\<^bsub>P\<^esub> r'"

  1681 			using sym [OF a_assoc [of "lcoeff g (^) k' \<odot>\<^bsub>P\<^esub> (g \<otimes>\<^bsub>P\<^esub> ?q)" "g \<otimes>\<^bsub>P\<^esub> q'" "r'"]]

  1682 			using q'_in_carrier r'_in_carrier by simp

  1683 		      also have "\<dots> = (lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> (?q \<otimes>\<^bsub>P\<^esub> g) \<oplus>\<^bsub>P\<^esub> q' \<otimes>\<^bsub>P\<^esub> g \<oplus>\<^bsub>P\<^esub> r'"

  1684 			using q'_in_carrier by (auto simp add: m_comm)

  1685 		      also have "\<dots> = (((lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> ?q) \<otimes>\<^bsub>P\<^esub> g) \<oplus>\<^bsub>P\<^esub> q' \<otimes>\<^bsub>P\<^esub> g \<oplus>\<^bsub>P\<^esub> r'"

  1686 			using smult_assoc2 q'_in_carrier by auto

  1687 		      also have "\<dots> = ((lcoeff g (^) k') \<odot>\<^bsub>P\<^esub> ?q \<oplus>\<^bsub>P\<^esub> q') \<otimes>\<^bsub>P\<^esub> g \<oplus>\<^bsub>P\<^esub> r'"

  1688 			using sym [OF l_distr] and q'_in_carrier by auto

  1689 		      finally show ?thesis using m_comm q'_in_carrier by auto

  1690 		    qed

  1691 		  qed (simp_all add: rem_deg q'_in_carrier r'_in_carrier)

  1692 		}

  1693 	      qed

  1694 	    }

  1695 	  qed

  1696 	qed

  1697       qed

  1698     }

  1699   qed

  1700 qed

  1701

  1702 end

  1703

  1704

  1705 text {*The remainder theorem as corollary of the long division theorem.*}

  1706

  1707 context UP_cring

  1708 begin

  1709

  1710 lemma deg_minus_monom:

  1711   assumes a: "a \<in> carrier R"

  1712   and R_not_trivial: "(carrier R \<noteq> {\<zero>})"

  1713   shows "deg R (monom P \<one>\<^bsub>R\<^esub> 1 \<ominus>\<^bsub>P\<^esub> monom P a 0) = 1"

  1714   (is "deg R ?g = 1")

  1715 proof -

  1716   have "deg R ?g \<le> 1"

  1717   proof (rule deg_aboveI)

  1718     fix m

  1719     assume "(1::nat) < m"

  1720     then show "coeff P ?g m = \<zero>"

  1721       using coeff_minus using a by auto algebra

  1722   qed (simp add: a)

  1723   moreover have "deg R ?g \<ge> 1"

  1724   proof (rule deg_belowI)

  1725     show "coeff P ?g 1 \<noteq> \<zero>"

  1726       using a using R.carrier_one_not_zero R_not_trivial by simp algebra

  1727   qed (simp add: a)

  1728   ultimately show ?thesis by simp

  1729 qed

  1730

  1731 lemma lcoeff_monom:

  1732   assumes a: "a \<in> carrier R" and R_not_trivial: "(carrier R \<noteq> {\<zero>})"

  1733   shows "lcoeff (monom P \<one>\<^bsub>R\<^esub> 1 \<ominus>\<^bsub>P\<^esub> monom P a 0) = \<one>"

  1734   using deg_minus_monom [OF a R_not_trivial]

  1735   using coeff_minus a by auto algebra

  1736

  1737 lemma deg_nzero_nzero:

  1738   assumes deg_p_nzero: "deg R p \<noteq> 0"

  1739   shows "p \<noteq> \<zero>\<^bsub>P\<^esub>"

  1740   using deg_zero deg_p_nzero by auto

  1741

  1742 lemma deg_monom_minus:

  1743   assumes a: "a \<in> carrier R"

  1744   and R_not_trivial: "carrier R \<noteq> {\<zero>}"

  1745   shows "deg R (monom P \<one>\<^bsub>R\<^esub> 1 \<ominus>\<^bsub>P\<^esub> monom P a 0) = 1"

  1746   (is "deg R ?g = 1")

  1747 proof -

  1748   have "deg R ?g \<le> 1"

  1749   proof (rule deg_aboveI)

  1750     fix m::nat assume "1 < m" then show "coeff P ?g m = \<zero>"

  1751       using coeff_minus [OF monom_closed [OF R.one_closed, of 1] monom_closed [OF a, of 0], of m]

  1752       using coeff_monom [OF R.one_closed, of 1 m] using coeff_monom [OF a, of 0 m] by auto algebra

  1753   qed (simp add: a)

  1754   moreover have "1 \<le> deg R ?g"

  1755   proof (rule deg_belowI)

  1756     show "coeff P ?g 1 \<noteq> \<zero>"

  1757       using coeff_minus [OF monom_closed [OF R.one_closed, of 1] monom_closed [OF a, of 0], of 1]

  1758       using coeff_monom [OF R.one_closed, of 1 1] using coeff_monom [OF a, of 0 1]

  1759       using R_not_trivial using R.carrier_one_not_zero

  1760       by auto algebra

  1761   qed (simp add: a)

  1762   ultimately show ?thesis by simp

  1763 qed

  1764

  1765 lemma eval_monom_expr:

  1766   assumes a: "a \<in> carrier R"

  1767   shows "eval R R id a (monom P \<one>\<^bsub>R\<^esub> 1 \<ominus>\<^bsub>P\<^esub> monom P a 0) = \<zero>"

  1768   (is "eval R R id a ?g = _")

  1769 proof -

  1770   interpret UP_pre_univ_prop R R id proof qed simp

  1771   have eval_ring_hom: "eval R R id a \<in> ring_hom P R" using eval_ring_hom [OF a] by simp

  1772   interpret ring_hom_cring P R "eval R R id a" proof qed (simp add: eval_ring_hom)

  1773   have mon1_closed: "monom P \<one>\<^bsub>R\<^esub> 1 \<in> carrier P"

  1774     and mon0_closed: "monom P a 0 \<in> carrier P"

  1775     and min_mon0_closed: "\<ominus>\<^bsub>P\<^esub> monom P a 0 \<in> carrier P"

  1776     using a R.a_inv_closed by auto

  1777   have "eval R R id a ?g = eval R R id a (monom P \<one> 1) \<ominus> eval R R id a (monom P a 0)"

  1778     unfolding P.minus_eq [OF mon1_closed mon0_closed]

  1779     unfolding hom_add [OF mon1_closed min_mon0_closed]

  1780     unfolding hom_a_inv [OF mon0_closed]

  1781     using R.minus_eq [symmetric] mon1_closed mon0_closed by auto

  1782   also have "\<dots> = a \<ominus> a"

  1783     using eval_monom [OF R.one_closed a, of 1] using eval_monom [OF a a, of 0] using a by simp

  1784   also have "\<dots> = \<zero>"

  1785     using a by algebra

  1786   finally show ?thesis by simp

  1787 qed

  1788

  1789 lemma remainder_theorem_exist:

  1790   assumes f: "f \<in> carrier P" and a: "a \<in> carrier R"

  1791   and R_not_trivial: "carrier R \<noteq> {\<zero>}"

  1792   shows "\<exists> q r. (q \<in> carrier P) \<and> (r \<in> carrier P) \<and> f = (monom P \<one>\<^bsub>R\<^esub> 1 \<ominus>\<^bsub>P\<^esub> monom P a 0) \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r \<and> (deg R r = 0)"

  1793   (is "\<exists> q r. (q \<in> carrier P) \<and> (r \<in> carrier P) \<and> f = ?g \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r \<and> (deg R r = 0)")

  1794 proof -

  1795   let ?g = "monom P \<one>\<^bsub>R\<^esub> 1 \<ominus>\<^bsub>P\<^esub> monom P a 0"

  1796   from deg_minus_monom [OF a R_not_trivial]

  1797   have deg_g_nzero: "deg R ?g \<noteq> 0" by simp

  1798   have "\<exists>q r (k::nat). q \<in> carrier P \<and> r \<in> carrier P \<and>

  1799     lcoeff ?g (^) k \<odot>\<^bsub>P\<^esub> f = ?g \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r \<and> (r = \<zero>\<^bsub>P\<^esub> \<or> deg R r < deg R ?g)"

  1800     using long_div_theorem [OF _ f deg_nzero_nzero [OF deg_g_nzero]] a

  1801     by auto

  1802   then show ?thesis

  1803     unfolding lcoeff_monom [OF a R_not_trivial]

  1804     unfolding deg_monom_minus [OF a R_not_trivial]

  1805     using smult_one [OF f] using deg_zero by force

  1806 qed

  1807

  1808 lemma remainder_theorem_expression:

  1809   assumes f [simp]: "f \<in> carrier P" and a [simp]: "a \<in> carrier R"

  1810   and q [simp]: "q \<in> carrier P" and r [simp]: "r \<in> carrier P"

  1811   and R_not_trivial: "carrier R \<noteq> {\<zero>}"

  1812   and f_expr: "f = (monom P \<one>\<^bsub>R\<^esub> 1 \<ominus>\<^bsub>P\<^esub> monom P a 0) \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r"

  1813   (is "f = ?g \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r" is "f = ?gq \<oplus>\<^bsub>P\<^esub> r")

  1814     and deg_r_0: "deg R r = 0"

  1815     shows "r = monom P (eval R R id a f) 0"

  1816 proof -

  1817   interpret UP_pre_univ_prop R R id P proof qed simp

  1818   have eval_ring_hom: "eval R R id a \<in> ring_hom P R"

  1819     using eval_ring_hom [OF a] by simp

  1820   have "eval R R id a f = eval R R id a ?gq \<oplus>\<^bsub>R\<^esub> eval R R id a r"

  1821     unfolding f_expr using ring_hom_add [OF eval_ring_hom] by auto

  1822   also have "\<dots> = ((eval R R id a ?g) \<otimes> (eval R R id a q)) \<oplus>\<^bsub>R\<^esub> eval R R id a r"

  1823     using ring_hom_mult [OF eval_ring_hom] by auto

  1824   also have "\<dots> = \<zero> \<oplus> eval R R id a r"

  1825     unfolding eval_monom_expr [OF a] using eval_ring_hom

  1826     unfolding ring_hom_def using q unfolding Pi_def by simp

  1827   also have "\<dots> = eval R R id a r"

  1828     using eval_ring_hom unfolding ring_hom_def using r unfolding Pi_def by simp

  1829   finally have eval_eq: "eval R R id a f = eval R R id a r" by simp

  1830   from deg_zero_impl_monom [OF r deg_r_0]

  1831   have "r = monom P (coeff P r 0) 0" by simp

  1832   with eval_const [OF a, of "coeff P r 0"] eval_eq

  1833   show ?thesis by auto

  1834 qed

  1835

  1836 corollary remainder_theorem:

  1837   assumes f [simp]: "f \<in> carrier P" and a [simp]: "a \<in> carrier R"

  1838   and R_not_trivial: "carrier R \<noteq> {\<zero>}"

  1839   shows "\<exists> q r. (q \<in> carrier P) \<and> (r \<in> carrier P) \<and>

  1840      f = (monom P \<one>\<^bsub>R\<^esub> 1 \<ominus>\<^bsub>P\<^esub> monom P a 0) \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> monom P (eval R R id a f) 0"

  1841   (is "\<exists> q r. (q \<in> carrier P) \<and> (r \<in> carrier P) \<and> f = ?g \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> monom P (eval R R id a f) 0")

  1842 proof -

  1843   from remainder_theorem_exist [OF f a R_not_trivial]

  1844   obtain q r

  1845     where q_r: "q \<in> carrier P \<and> r \<in> carrier P \<and> f = ?g \<otimes>\<^bsub>P\<^esub> q \<oplus>\<^bsub>P\<^esub> r"

  1846     and deg_r: "deg R r = 0" by force

  1847   with remainder_theorem_expression [OF f a _ _ R_not_trivial, of q r]

  1848   show ?thesis by auto

  1849 qed

  1850

  1851 end

  1852

  1853

  1854 subsection {* Sample Application of Evaluation Homomorphism *}

  1855

  1856 lemma UP_pre_univ_propI:

  1857   assumes "cring R"

  1858     and "cring S"

  1859     and "h \<in> ring_hom R S"

  1860   shows "UP_pre_univ_prop R S h"

  1861   using assms

  1862   by (auto intro!: UP_pre_univ_prop.intro ring_hom_cring.intro

  1863     ring_hom_cring_axioms.intro UP_cring.intro)

  1864

  1865 definition  INTEG :: "int ring"

  1866   where INTEG_def: "INTEG == (| carrier = UNIV, mult = op *, one = 1, zero = 0, add = op + |)"

  1867

  1868 lemma INTEG_cring:

  1869   "cring INTEG"

  1870   by (unfold INTEG_def) (auto intro!: cringI abelian_groupI comm_monoidI

  1871     zadd_zminus_inverse2 zadd_zmult_distrib)

  1872

  1873 lemma INTEG_id_eval:

  1874   "UP_pre_univ_prop INTEG INTEG id"

  1875   by (fast intro: UP_pre_univ_propI INTEG_cring id_ring_hom)

  1876

  1877 text {*

  1878   Interpretation now enables to import all theorems and lemmas

  1879   valid in the context of homomorphisms between @{term INTEG} and @{term

  1880   "UP INTEG"} globally.

  1881 *}

  1882

  1883 interpretation INTEG: UP_pre_univ_prop INTEG INTEG id "UP INTEG"

  1884   using INTEG_id_eval by simp_all

  1885

  1886 lemma INTEG_closed [intro, simp]:

  1887   "z \<in> carrier INTEG"

  1888   by (unfold INTEG_def) simp

  1889

  1890 lemma INTEG_mult [simp]:

  1891   "mult INTEG z w = z * w"

  1892   by (unfold INTEG_def) simp

  1893

  1894 lemma INTEG_pow [simp]:

  1895   "pow INTEG z n = z ^ n"

  1896   by (induct n) (simp_all add: INTEG_def nat_pow_def)

  1897

  1898 lemma "eval INTEG INTEG id 10 (monom (UP INTEG) 5 2) = 500"

  1899   by (simp add: INTEG.eval_monom)

  1900

  1901 end