src/HOL/NumberTheory/Chinese.thy
 author nipkow Thu, 30 May 2002 10:12:52 +0200 changeset 13187 e5434b822a96 parent 11868 56db9f3a6b3e child 13524 604d0f3622d6 permissions -rw-r--r--
Modifications due to enhanced linear arithmetic.
```
(*  Title:      HOL/NumberTheory/Chinese.thy
ID:         \$Id\$
Author:     Thomas M. Rasmussen
*)

header {* The Chinese Remainder Theorem *}

theory Chinese = IntPrimes:

text {*
The Chinese Remainder Theorem for an arbitrary finite number of
equations.  (The one-equation case is included in theory @{text
IntPrimes}.  Uses functions for indexing.\footnote{Maybe @{term
funprod} and @{term funsum} should be based on general @{term fold}
on indices?}
*}

subsection {* Definitions *}

consts
funprod :: "(nat => int) => nat => nat => int"
funsum :: "(nat => int) => nat => nat => int"

primrec
"funprod f i 0 = f i"
"funprod f i (Suc n) = f (Suc (i + n)) * funprod f i n"

primrec
"funsum f i 0 = f i"
"funsum f i (Suc n) = f (Suc (i + n)) + funsum f i n"

consts
m_cond :: "nat => (nat => int) => bool"
km_cond :: "nat => (nat => int) => (nat => int) => bool"
lincong_sol ::
"nat => (nat => int) => (nat => int) => (nat => int) => int => bool"

mhf :: "(nat => int) => nat => nat => int"
xilin_sol ::
"nat => nat => (nat => int) => (nat => int) => (nat => int) => int"
x_sol :: "nat => (nat => int) => (nat => int) => (nat => int) => int"

defs
m_cond_def:
"m_cond n mf ==
(\<forall>i. i \<le> n --> 0 < mf i) \<and>
(\<forall>i j. i \<le> n \<and> j \<le> n \<and> i \<noteq> j --> zgcd (mf i, mf j) = 1)"

km_cond_def:
"km_cond n kf mf == \<forall>i. i \<le> n --> zgcd (kf i, mf i) = 1"

lincong_sol_def:
"lincong_sol n kf bf mf x == \<forall>i. i \<le> n --> zcong (kf i * x) (bf i) (mf i)"

mhf_def:
"mhf mf n i ==
if i = 0 then funprod mf (Suc 0) (n - Suc 0)
else if i = n then funprod mf 0 (n - Suc 0)
else funprod mf 0 (i - Suc 0) * funprod mf (Suc i) (n - Suc 0 - i)"

xilin_sol_def:
"xilin_sol i n kf bf mf ==
if 0 < n \<and> i \<le> n \<and> m_cond n mf \<and> km_cond n kf mf then
(SOME x. 0 \<le> x \<and> x < mf i \<and> zcong (kf i * mhf mf n i * x) (bf i) (mf i))
else 0"

x_sol_def:
"x_sol n kf bf mf == funsum (\<lambda>i. xilin_sol i n kf bf mf * mhf mf n i) 0 n"

text {* \medskip @{term funprod} and @{term funsum} *}

lemma funprod_pos: "(\<forall>i. i \<le> n --> 0 < mf i) ==> 0 < funprod mf 0 n"
apply (induct n)
apply auto
done

lemma funprod_zgcd [rule_format (no_asm)]:
"(\<forall>i. k \<le> i \<and> i \<le> k + l --> zgcd (mf i, mf m) = 1) -->
zgcd (funprod mf k l, mf m) = 1"
apply (induct l)
apply simp_all
apply (rule impI)+
apply (subst zgcd_zmult_cancel)
apply auto
done

lemma funprod_zdvd [rule_format]:
"k \<le> i --> i \<le> k + l --> mf i dvd funprod mf k l"
apply (induct l)
apply auto
apply (rule_tac [2] zdvd_zmult2)
apply (rule_tac [3] zdvd_zmult)
apply (subgoal_tac "i = k")
apply (subgoal_tac [3] "i = Suc (k + n)")
apply (simp_all (no_asm_simp))
done

lemma funsum_mod:
"funsum f k l mod m = funsum (\<lambda>i. (f i) mod m) k l mod m"
apply (induct l)
apply auto
apply (rule trans)
apply simp
done

lemma funsum_zero [rule_format (no_asm)]:
"(\<forall>i. k \<le> i \<and> i \<le> k + l --> f i = 0) --> (funsum f k l) = 0"
apply (induct l)
apply auto
done

lemma funsum_oneelem [rule_format (no_asm)]:
"k \<le> j --> j \<le> k + l -->
(\<forall>i. k \<le> i \<and> i \<le> k + l \<and> i \<noteq> j --> f i = 0) -->
funsum f k l = f j"
apply (induct l)
prefer 2
apply clarify
defer
apply clarify
apply (subgoal_tac "k = j")
apply (simp_all (no_asm_simp))
apply (case_tac "Suc (k + n) = j")
apply (subgoal_tac "funsum f k n = 0")
apply (rule_tac [2] funsum_zero)
apply (subgoal_tac [3] "f (Suc (k + n)) = 0")
apply (subgoal_tac [3] "j \<le> k + n")
prefer 4
apply arith
apply auto
done

subsection {* Chinese: uniqueness *}

lemma aux:
"m_cond n mf ==> km_cond n kf mf
==> lincong_sol n kf bf mf x ==> lincong_sol n kf bf mf y
==> [x = y] (mod mf n)"
apply (unfold m_cond_def km_cond_def lincong_sol_def)
apply (rule iffD1)
apply (rule_tac k = "kf n" in zcong_cancel2)
apply (rule_tac [3] b = "bf n" in zcong_trans)
prefer 4
apply (subst zcong_sym)
defer
apply (rule order_less_imp_le)
apply simp_all
done

lemma zcong_funprod [rule_format]:
"m_cond n mf --> km_cond n kf mf -->
lincong_sol n kf bf mf x --> lincong_sol n kf bf mf y -->
[x = y] (mod funprod mf 0 n)"
apply (induct n)
apply (simp_all (no_asm))
apply (blast intro: aux)
apply (rule impI)+
apply (rule zcong_zgcd_zmult_zmod)
apply (blast intro: aux)
prefer 2
apply (subst zgcd_commute)
apply (rule funprod_zgcd)
apply (auto simp add: m_cond_def km_cond_def lincong_sol_def)
done

subsection {* Chinese: existence *}

lemma unique_xi_sol:
"0 < n ==> i \<le> n ==> m_cond n mf ==> km_cond n kf mf
==> \<exists>!x. 0 \<le> x \<and> x < mf i \<and> [kf i * mhf mf n i * x = bf i] (mod mf i)"
apply (rule zcong_lineq_unique)
apply (tactic {* stac (thm "zgcd_zmult_cancel") 2 *})
apply (unfold m_cond_def km_cond_def mhf_def)
apply (simp_all (no_asm_simp))
apply safe
apply (tactic {* stac (thm "zgcd_zmult_cancel") 3 *})
apply (rule_tac [!] funprod_zgcd)
apply safe
apply simp_all
apply (subgoal_tac "i<n")
prefer 2
apply arith
apply (case_tac [2] i)
apply simp_all
done

lemma aux:
"0 < n ==> i \<le> n ==> j \<le> n ==> j \<noteq> i ==> mf j dvd mhf mf n i"
apply (unfold mhf_def)
apply (case_tac "i = 0")
apply (case_tac [2] "i = n")
apply (simp_all (no_asm_simp))
apply (case_tac [3] "j < i")
apply (rule_tac [3] zdvd_zmult2)
apply (rule_tac [4] zdvd_zmult)
apply (rule_tac [!] funprod_zdvd)
apply arith+
done

lemma x_sol_lin:
"0 < n ==> i \<le> n
==> x_sol n kf bf mf mod mf i =
xilin_sol i n kf bf mf * mhf mf n i mod mf i"
apply (unfold x_sol_def)
apply (subst funsum_mod)
apply (subst funsum_oneelem)
apply auto
apply (subst zdvd_iff_zmod_eq_0 [symmetric])
apply (rule zdvd_zmult)
apply (rule aux)
apply auto
done

subsection {* Chinese *}

lemma chinese_remainder:
"0 < n ==> m_cond n mf ==> km_cond n kf mf
==> \<exists>!x. 0 \<le> x \<and> x < funprod mf 0 n \<and> lincong_sol n kf bf mf x"
apply safe
apply (rule_tac [2] m = "funprod mf 0 n" in zcong_zless_imp_eq)
apply (rule_tac [6] zcong_funprod)
apply auto
apply (rule_tac x = "x_sol n kf bf mf mod funprod mf 0 n" in exI)
apply (unfold lincong_sol_def)
apply safe
apply (tactic {* stac (thm "zcong_zmod") 3 *})
apply (tactic {* stac (thm "zmod_zmult_distrib") 3 *})
apply (tactic {* stac (thm "zmod_zdvd_zmod") 3 *})
apply (tactic {* stac (thm "x_sol_lin") 5 *})
apply (tactic {* stac (thm "zmod_zmult_distrib" RS sym) 7 *})
apply (tactic {* stac (thm "zcong_zmod" RS sym) 7 *})
apply (subgoal_tac [7]
"0 \<le> xilin_sol i n kf bf mf \<and> xilin_sol i n kf bf mf < mf i
\<and> [kf i * mhf mf n i * xilin_sol i n kf bf mf = bf i] (mod mf i)")
prefer 7