author chaieb Mon, 25 Feb 2008 11:27:25 +0100 changeset 26123 44384b5c4fc0 parent 26122 76cbf193c09d child 26124 2514f0ade8bc
A proof a the fundamental theorem of algebra
```--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/Complex/Fundamental_Theorem_Algebra.thy	Mon Feb 25 11:27:25 2008 +0100
@@ -0,0 +1,1370 @@
+(*  Title:       Fundamental_Theorem_Algebra.thy
+    ID:          \$Id\$
+    Author:      Amine Chaieb
+*)
+
+
+theory Fundamental_Theorem_Algebra
+  imports  Univ_Poly Complex
+begin
+
+section {* Square root of complex numbers *}
+definition csqrt :: "complex \<Rightarrow> complex" where
+"csqrt z = (if Im z = 0 then
+            if 0 \<le> Re z then Complex (sqrt(Re z)) 0
+            else Complex 0 (sqrt(- Re z))
+           else Complex (sqrt((cmod z + Re z) /2))
+                        ((Im z / abs(Im z)) * sqrt((cmod z - Re z) /2)))"
+
+lemma csqrt: "csqrt z ^ 2 = z"
+proof-
+  obtain x y where xy: "z = Complex x y" by (cases z, simp_all)
+  {assume y0: "y = 0"
+    {assume x0: "x \<ge> 0"
+      then have ?thesis using y0 xy real_sqrt_pow2[OF x0]
+	by (simp add: csqrt_def power2_eq_square)}
+    moreover
+    {assume "\<not> x \<ge> 0" hence x0: "- x \<ge> 0" by arith
+      then have ?thesis using y0 xy real_sqrt_pow2[OF x0]
+	by (simp add: csqrt_def power2_eq_square) }
+    ultimately have ?thesis by blast}
+  moreover
+  {assume y0: "y\<noteq>0"
+    {fix x y
+      let ?z = "Complex x y"
+      from abs_Re_le_cmod[of ?z] have tha: "abs x \<le> cmod ?z" by auto
+      hence "cmod ?z - x \<ge> 0" "cmod ?z + x \<ge> 0" by (cases "x \<ge> 0", arith+)
+      hence "(sqrt (x * x + y * y) + x) / 2 \<ge> 0" "(sqrt (x * x + y * y) - x) / 2 \<ge> 0" by (simp_all add: power2_eq_square) }
+    note th = this
+    have sq4: "\<And>x::real. x^2 / 4 = (x / 2) ^ 2"
+    from th[of x y]
+    have sq4': "sqrt (((sqrt (x * x + y * y) + x)^2 / 4)) = (sqrt (x * x + y * y) + x) / 2" "sqrt (((sqrt (x * x + y * y) - x)^2 / 4)) = (sqrt (x * x + y * y) - x) / 2" unfolding sq4 by simp_all
+    then have th1: "sqrt ((sqrt (x * x + y * y) + x) * (sqrt (x * x + y * y) + x) / 4) - sqrt ((sqrt (x * x + y * y) - x) * (sqrt (x * x + y * y) - x) / 4) = x"
+      unfolding power2_eq_square by simp
+    have "sqrt 4 = sqrt (2^2)" by simp
+    hence sqrt4: "sqrt 4 = 2" by (simp only: real_sqrt_abs)
+    have th2: "2 *(y * sqrt ((sqrt (x * x + y * y) - x) * (sqrt (x * x + y * y) + x) / 4)) / \<bar>y\<bar> = y"
+      using iffD2[OF real_sqrt_pow2_iff sum_power2_ge_zero[of x y]] y0
+      unfolding power2_eq_square
+      by (simp add: ring_simps real_sqrt_divide sqrt4)
+     from y0 xy have ?thesis  apply (simp add: csqrt_def power2_eq_square)
+       apply (simp add: real_sqrt_sum_squares_mult_ge_zero[of x y] real_sqrt_pow2[OF th(1)[of x y], unfolded power2_eq_square] real_sqrt_pow2[OF th(2)[of x y], unfolded power2_eq_square] real_sqrt_mult[symmetric])
+      using th1 th2  ..}
+  ultimately show ?thesis by blast
+qed
+
+
+section{* More lemmas about module of complex numbers *}
+
+lemma complex_of_real_power: "complex_of_real x ^ n = complex_of_real (x^n)"
+  by (induct n, auto)
+
+lemma cmod_pos: "cmod z \<ge> 0" by simp
+lemma complex_mod_triangle_ineq: "cmod (z + w) \<le> cmod z + cmod w"
+  using complex_mod_triangle_ineq2[of z w] by (simp add: ring_simps)
+
+lemma cmod_mult: "cmod (z*w) = cmod z * cmod w"
+proof-
+  from rcis_Ex[of z] rcis_Ex[of w]
+  obtain rz az rw aw where z: "z = rcis rz az" and w: "w = rcis rw aw"  by blast
+  thus ?thesis by (simp add: rcis_mult abs_mult)
+qed
+
+lemma cmod_divide: "cmod (z/w) = cmod z / cmod w"
+proof-
+  from rcis_Ex[of z] rcis_Ex[of w]
+  obtain rz az rw aw where z: "z = rcis rz az" and w: "w = rcis rw aw"  by blast
+  thus ?thesis by (simp add: rcis_divide)
+qed
+
+lemma cmod_inverse: "cmod (inverse z) = inverse (cmod z)"
+  using cmod_divide[of 1 z] by (simp add: inverse_eq_divide)
+
+lemma cmod_uminus: "cmod (- z) = cmod z"
+  unfolding cmod_def by simp
+lemma cmod_abs_norm: "\<bar>cmod w - cmod z\<bar> \<le> cmod (w - z)"
+proof-
+  have ath: "\<And>(a::real) b x. a - b <= x \<Longrightarrow> b - a <= x ==> abs(a - b) <= x"
+    by arith
+  from complex_mod_triangle_ineq2[of "w - z" z]
+  have th1: "cmod w - cmod z \<le> cmod (w - z)" by simp
+  from complex_mod_triangle_ineq2[of "- (w - z)" "w"]
+  have th2: "cmod z - cmod w \<le> cmod (w - z)" using cmod_uminus [of "w - z"]
+    by simp
+  from ath[OF th1 th2] show ?thesis .
+qed
+
+lemma cmod_power: "cmod (z ^n) = cmod z ^ n" by (induct n, auto simp add: cmod_mult)
+lemma real_down2: "(0::real) < d1 \<Longrightarrow> 0 < d2 ==> EX e. 0 < e & e < d1 & e < d2"
+  apply ferrack apply arith done
+
+lemma cmod_complex_of_real: "cmod (complex_of_real x) = \<bar>x\<bar>"
+  unfolding cmod_def by auto
+
+
+text{* The triangle inequality for cmod *}
+lemma complex_mod_triangle_sub: "cmod w \<le> cmod (w + z) + norm z"
+  using complex_mod_triangle_ineq2[of "w + z" "-z"] by auto
+
+section{* Basic lemmas about complex polynomials *}
+
+lemma poly_bound_exists:
+  shows "\<exists>m. m > 0 \<and> (\<forall>z. cmod z <= r \<longrightarrow> cmod (poly p z) \<le> m)"
+proof(induct p)
+  case Nil thus ?case by (rule exI[where x=1], simp)
+next
+  case (Cons c cs)
+  from Cons.hyps obtain m where m: "\<forall>z. cmod z \<le> r \<longrightarrow> cmod (poly cs z) \<le> m"
+    by blast
+  let ?k = " 1 + cmod c + \<bar>r * m\<bar>"
+  have kp: "?k > 0" using abs_ge_zero[of "r*m"] cmod_pos[of c] by arith
+  {fix z
+    assume H: "cmod z \<le> r"
+    from m H have th: "cmod (poly cs z) \<le> m" by blast
+    from H have rp: "r \<ge> 0" using cmod_pos[of z] by arith
+    have "cmod (poly (c # cs) z) \<le> cmod c + cmod (z* poly cs z)"
+      using complex_mod_triangle_ineq[of c "z* poly cs z"] by simp
+    also have "\<dots> \<le> cmod c + r*m" using mult_mono[OF H th rp cmod_pos[of "poly cs z"]] by (simp add: cmod_mult)
+    also have "\<dots> \<le> ?k" by simp
+    finally have "cmod (poly (c # cs) z) \<le> ?k" .}
+  with kp show ?case by blast
+qed
+
+
+text{* Offsetting the variable in a polynomial gives another of same degree *}
+  (* FIXME : Lemma holds also in locale --- fix it laster *)
+lemma  poly_offset_lemma:
+  shows "\<exists>b q. (length q = length p) \<and> (\<forall>x. poly (b#q) (x::complex) = (a + x) * poly p x)"
+proof(induct p)
+  case Nil thus ?case by simp
+next
+  case (Cons c cs)
+  from Cons.hyps obtain b q where
+    bq: "length q = length cs" "\<forall>x. poly (b # q) x = (a + x) * poly cs x"
+    by blast
+  let ?b = "a*c"
+  let ?q = "(b+c)#q"
+  have lg: "length ?q = length (c#cs)" using bq(1) by simp
+  {fix x
+    from bq(2)[rule_format, of x]
+    have "x*poly (b # q) x = x*((a + x) * poly cs x)" by simp
+    hence "poly (?b# ?q) x = (a + x) * poly (c # cs) x"
+  with lg  show ?case by blast
+qed
+
+    (* FIXME : This one too*)
+lemma poly_offset: "\<exists> q. length q = length p \<and> (\<forall>x. poly q (x::complex) = poly p (a + x))"
+proof (induct p)
+  case Nil thus ?case by simp
+next
+  case (Cons c cs)
+  from Cons.hyps obtain q where q: "length q = length cs" "\<forall>x. poly q x = poly cs (a + x)" by blast
+  from poly_offset_lemma[of q a] obtain b p where
+    bp: "length p = length q" "\<forall>x. poly (b # p) x = (a + x) * poly q x"
+    by blast
+  thus ?case using q bp by - (rule exI[where x="(c + b)#p"], simp)
+qed
+
+text{* An alternative useful formulation of completeness of the reals *}
+lemma real_sup_exists: assumes ex: "\<exists>x. P x" and bz: "\<exists>z. \<forall>x. P x \<longrightarrow> x < z"
+  shows "\<exists>(s::real). \<forall>y. (\<exists>x. P x \<and> y < x) \<longleftrightarrow> y < s"
+proof-
+  from ex bz obtain x Y where x: "P x" and Y: "\<And>x. P x \<Longrightarrow> x < Y"  by blast
+  from ex have thx:"\<exists>x. x \<in> Collect P" by blast
+  from bz have thY: "\<exists>Y. isUb UNIV (Collect P) Y"
+    by(auto simp add: isUb_def isLub_def setge_def setle_def leastP_def Ball_def order_le_less)
+  from reals_complete[OF thx thY] obtain L where L: "isLub UNIV (Collect P) L"
+    by blast
+  from Y[OF x] have xY: "x < Y" .
+  from L have L': "\<forall>x. P x \<longrightarrow> x \<le> L" by (auto simp add: isUb_def isLub_def setge_def setle_def leastP_def Ball_def)
+  from Y have Y': "\<forall>x. P x \<longrightarrow> x \<le> Y"
+    apply (clarsimp, atomize (full)) by auto
+  from L Y' have "L \<le> Y" by (auto simp add: isUb_def isLub_def setge_def setle_def leastP_def Ball_def)
+  {fix y
+    {fix z assume z: "P z" "y < z"
+      from L' z have "y < L" by auto }
+    moreover
+    {assume yL: "y < L" "\<forall>z. P z \<longrightarrow> \<not> y < z"
+      hence nox: "\<forall>z. P z \<longrightarrow> y \<ge> z" by auto
+      from nox L have "y \<ge> L" by (auto simp add: isUb_def isLub_def setge_def setle_def leastP_def Ball_def)
+      with yL(1) have False  by arith}
+    ultimately have "(\<exists>x. P x \<and> y < x) \<longleftrightarrow> y < L" by blast}
+  thus ?thesis by blast
+qed
+
+
+text{* Given a binary function @{text "f:: nat \<Rightarrow> 'a \<Rightarrow> 'a"}, its values are uniquely determined by a function g *}
+
+lemma num_Axiom: "EX! g. g 0 = e \<and> (\<forall>n. g (Suc n) = f n (g n))"
+  unfolding Ex1_def
+  apply (rule_tac x="nat_rec e f" in exI)
+  apply (rule conjI)+
+apply (rule def_nat_rec_0, simp)
+apply (rule allI, rule def_nat_rec_Suc, simp)
+apply (rule allI, rule impI, rule ext)
+apply (erule conjE)
+apply (induct_tac x)
+apply (erule_tac x="n" in allE)
+apply (simp)
+done
+
+ text{* An equivalent formulation of monotony -- Not used here, but might be useful *}
+lemma mono_Suc: "mono f = (\<forall>n. (f n :: 'a :: order) \<le> f (Suc n))"
+unfolding mono_def
+proof auto
+  fix A B :: nat
+  assume H: "\<forall>n. f n \<le> f (Suc n)" "A \<le> B"
+  hence "\<exists>k. B = A + k" apply -  apply (thin_tac "\<forall>n. f n \<le> f (Suc n)")
+    by presburger
+  then obtain k where k: "B = A + k" by blast
+  {fix a k
+    have "f a \<le> f (a + k)"
+    proof (induct k)
+      case 0 thus ?case by simp
+    next
+      case (Suc k)
+      from Suc.hyps H(1)[rule_format, of "a + k"] show ?case by simp
+    qed}
+  with k show "f A \<le> f B" by blast
+qed
+
+text{* for any sequence, there is a mootonic subsequence *}
+lemma seq_monosub: "\<exists>f. subseq f \<and> monoseq (\<lambda> n. (s (f n)))"
+proof-
+  {assume H: "\<forall>n. \<exists>p >n. \<forall> m\<ge>p. s m \<le> s p"
+    let ?P = "\<lambda> p n. p > n \<and> (\<forall>m \<ge> p. s m \<le> s p)"
+    from num_Axiom[of "SOME p. ?P p 0" "\<lambda>p n. SOME p. ?P p n"]
+    obtain f where f: "f 0 = (SOME p. ?P p 0)" "\<forall>n. f (Suc n) = (SOME p. ?P p (f n))" by blast
+    have "?P (f 0) 0"  unfolding f(1) some_eq_ex[of "\<lambda>p. ?P p 0"]
+      using H apply -
+      apply (erule allE[where x=0], erule exE, rule_tac x="p" in exI)
+      unfolding order_le_less by blast
+    hence f0: "f 0 > 0" "\<forall>m \<ge> f 0. s m \<le> s (f 0)" by blast+
+    {fix n
+      have "?P (f (Suc n)) (f n)"
+	unfolding f(2)[rule_format, of n] some_eq_ex[of "\<lambda>p. ?P p (f n)"]
+	using H apply -
+      apply (erule allE[where x="f n"], erule exE, rule_tac x="p" in exI)
+      unfolding order_le_less by blast
+    hence "f (Suc n) > f n" "\<forall>m \<ge> f (Suc n). s m \<le> s (f (Suc n))" by blast+}
+  note fSuc = this
+    {fix p q assume pq: "p \<ge> f q"
+      have "s p \<le> s(f(q))"  using f0(2)[rule_format, of p] pq fSuc
+	by (cases q, simp_all) }
+    note pqth = this
+    {fix q
+      have "f (Suc q) > f q" apply (induct q)
+	using f0(1) fSuc(1)[of 0] apply simp by (rule fSuc(1))}
+    note fss = this
+    from fss have th1: "subseq f" unfolding subseq_Suc_iff ..
+    {fix a b
+      have "f a \<le> f (a + b)"
+      proof(induct b)
+	case 0 thus ?case by simp
+      next
+	case (Suc b)
+	from fSuc(1)[of "a + b"] Suc.hyps show ?case by simp
+      qed}
+    note fmon0 = this
+    have "monoseq (\<lambda>n. s (f n))"
+    proof-
+      {fix n
+	have "s (f n) \<ge> s (f (Suc n))"
+	proof(cases n)
+	  case 0
+	  assume n0: "n = 0"
+	  from fSuc(1)[of 0] have th0: "f 0 \<le> f (Suc 0)" by simp
+	  from f0(2)[rule_format, OF th0] show ?thesis  using n0 by simp
+	next
+	  case (Suc m)
+	  assume m: "n = Suc m"
+	  from fSuc(1)[of n] m have th0: "f (Suc m) \<le> f (Suc (Suc m))" by simp
+	  from m fSuc(2)[rule_format, OF th0] show ?thesis by simp
+	qed}
+      thus "monoseq (\<lambda>n. s (f n))" unfolding monoseq_Suc by blast
+    qed
+    with th1 have ?thesis by blast}
+  moreover
+  {fix N assume N: "\<forall>p >N. \<exists> m\<ge>p. s m > s p"
+    {fix p assume p: "p \<ge> Suc N"
+      hence pN: "p > N" by arith with N obtain m where m: "m \<ge> p" "s m > s p" by blast
+      have "m \<noteq> p" using m(2) by auto
+      with m have "\<exists>m>p. s p < s m" by - (rule exI[where x=m], auto)}
+    note th0 = this
+    let ?P = "\<lambda>m x. m > x \<and> s x < s m"
+    from num_Axiom[of "SOME x. ?P x (Suc N)" "\<lambda>m x. SOME y. ?P y x"]
+    obtain f where f: "f 0 = (SOME x. ?P x (Suc N))"
+      "\<forall>n. f (Suc n) = (SOME m. ?P m (f n))" by blast
+    have "?P (f 0) (Suc N)"  unfolding f(1) some_eq_ex[of "\<lambda>p. ?P p (Suc N)"]
+      using N apply -
+      apply (erule allE[where x="Suc N"], clarsimp)
+      apply (rule_tac x="m" in exI)
+      apply auto
+      apply (subgoal_tac "Suc N \<noteq> m")
+      apply simp
+      apply (rule ccontr, simp)
+      done
+    hence f0: "f 0 > Suc N" "s (Suc N) < s (f 0)" by blast+
+    {fix n
+      have "f n > N \<and> ?P (f (Suc n)) (f n)"
+	unfolding f(2)[rule_format, of n] some_eq_ex[of "\<lambda>p. ?P p (f n)"]
+      proof (induct n)
+	case 0 thus ?case
+	  using f0 N apply auto
+	  apply (erule allE[where x="f 0"], clarsimp)
+	  apply (rule_tac x="m" in exI, simp)
+	  by (subgoal_tac "f 0 \<noteq> m", auto)
+      next
+	case (Suc n)
+	from Suc.hyps have Nfn: "N < f n" by blast
+	from Suc.hyps obtain m where m: "m > f n" "s (f n) < s m" by blast
+	with Nfn have mN: "m > N" by arith
+	note key = Suc.hyps[unfolded some_eq_ex[of "\<lambda>p. ?P p (f n)", symmetric] f(2)[rule_format, of n, symmetric]]
+
+	from key have th0: "f (Suc n) > N" by simp
+	from N[rule_format, OF th0]
+	obtain m' where m': "m' \<ge> f (Suc n)" "s (f (Suc n)) < s m'" by blast
+	have "m' \<noteq> f (Suc (n))" apply (rule ccontr) using m'(2) by auto
+	hence "m' > f (Suc n)" using m'(1) by simp
+	with key m'(2) show ?case by auto
+      qed}
+    note fSuc = this
+    {fix n
+      have "f n \<ge> Suc N \<and> f(Suc n) > f n \<and> s(f n) < s(f(Suc n))" using fSuc[of n] by auto
+      hence "f n \<ge> Suc N" "f(Suc n) > f n" "s(f n) < s(f(Suc n))" by blast+}
+    note thf = this
+    have sqf: "subseq f" unfolding subseq_Suc_iff using thf by simp
+    have "monoseq (\<lambda>n. s (f n))"  unfolding monoseq_Suc using thf
+      apply -
+      apply (rule disjI1)
+      apply auto
+      apply (rule order_less_imp_le)
+      apply blast
+      done
+    then have ?thesis  using sqf by blast}
+  ultimately show ?thesis unfolding linorder_not_less[symmetric] by blast
+qed
+
+lemma seq_suble: assumes sf: "subseq f" shows "n \<le> f n"
+proof(induct n)
+  case 0 thus ?case by simp
+next
+  case (Suc n)
+  from sf[unfolded subseq_Suc_iff, rule_format, of n] Suc.hyps
+  have "n < f (Suc n)" by arith
+  thus ?case by arith
+qed
+
+section {* Fundamental theorem of algebra *}
+lemma  unimodular_reduce_norm:
+  assumes md: "cmod z = 1"
+  shows "cmod (z + 1) < 1 \<or> cmod (z - 1) < 1 \<or> cmod (z + ii) < 1 \<or> cmod (z - ii) < 1"
+proof-
+  obtain x y where z: "z = Complex x y " by (cases z, auto)
+  from md z have xy: "x^2 + y^2 = 1" by (simp add: cmod_def)
+  {assume C: "cmod (z + 1) \<ge> 1" "cmod (z - 1) \<ge> 1" "cmod (z + ii) \<ge> 1" "cmod (z - ii) \<ge> 1"
+    from C z xy have "2*x \<le> 1" "2*x \<ge> -1" "2*y \<le> 1" "2*y \<ge> -1"
+      by (simp_all add: cmod_def power2_eq_square ring_simps)
+    hence "abs (2*x) \<le> 1" "abs (2*y) \<le> 1" by simp_all
+    hence "(abs (2 * x))^2 <= 1^2" "(abs (2 * y)) ^2 <= 1^2"
+      by - (rule power_mono, simp, simp)+
+    hence th0: "4*x^2 \<le> 1" "4*y^2 \<le> 1"
+      by (simp_all  add: power2_abs power_mult_distrib)
+    from add_mono[OF th0] xy have False by simp }
+  thus ?thesis unfolding linorder_not_le[symmetric] by blast
+qed
+
+text{* Hence we can always reduce modulus of 1 + b z^n if nonzero *}
+lemma reduce_poly_simple:
+ assumes b: "b \<noteq> 0" and n: "n\<noteq>0"
+  shows "\<exists>z. cmod (1 + b * z^n) < 1"
+using n
+proof(induct n rule: nat_less_induct)
+  fix n
+  assume IH: "\<forall>m<n. m \<noteq> 0 \<longrightarrow> (\<exists>z. cmod (1 + b * z ^ m) < 1)" and n: "n \<noteq> 0"
+  let ?P = "\<lambda>z n. cmod (1 + b * z ^ n) < 1"
+  {assume e: "even n"
+    hence "\<exists>m. n = 2*m" by presburger
+    then obtain m where m: "n = 2*m" by blast
+    from n m have "m\<noteq>0" "m < n" by presburger+
+    with IH[rule_format, of m] obtain z where z: "?P z m" by blast
+    from z have "?P (csqrt z) n" by (simp add: m power_mult csqrt)
+    hence "\<exists>z. ?P z n" ..}
+  moreover
+  {assume o: "odd n"
+    from b have b': "b^2 \<noteq> 0" unfolding power2_eq_square by simp
+    have "Im (inverse b) * (Im (inverse b) * \<bar>Im b * Im b + Re b * Re b\<bar>) +
+    Re (inverse b) * (Re (inverse b) * \<bar>Im b * Im b + Re b * Re b\<bar>) =
+    ((Re (inverse b))^2 + (Im (inverse b))^2) * \<bar>Im b * Im b + Re b * Re b\<bar>" by algebra
+    also have "\<dots> = cmod (inverse b) ^2 * cmod b ^ 2"
+    finally
+    have th0: "Im (inverse b) * (Im (inverse b) * \<bar>Im b * Im b + Re b * Re b\<bar>) +
+    Re (inverse b) * (Re (inverse b) * \<bar>Im b * Im b + Re b * Re b\<bar>) =
+    1"
+      apply (simp add: power2_eq_square cmod_mult[symmetric] cmod_inverse[symmetric])
+      using right_inverse[OF b']
+      by (simp add: power2_eq_square[symmetric] power_inverse[symmetric] ring_simps)
+    have th0: "cmod (complex_of_real (cmod b) / b) = 1"
+      apply (simp add: complex_Re_mult cmod_def power2_eq_square Re_complex_of_real Im_complex_of_real divide_inverse ring_simps )
+      by (simp add: real_sqrt_mult[symmetric] th0)
+    from o have "\<exists>m. n = Suc (2*m)" by presburger+
+    then obtain m where m: "n = Suc (2*m)" by blast
+    from unimodular_reduce_norm[OF th0] o
+    have "\<exists>v. cmod (complex_of_real (cmod b) / b + v^n) < 1"
+      apply (cases "cmod (complex_of_real (cmod b) / b + 1) < 1", rule_tac x="1" in exI, simp)
+      apply (cases "cmod (complex_of_real (cmod b) / b - 1) < 1", rule_tac x="-1" in exI, simp add: diff_def)
+      apply (cases "cmod (complex_of_real (cmod b) / b + ii) < 1")
+      apply (cases "even m", rule_tac x="ii" in exI, simp add: m power_mult)
+      apply (rule_tac x="- ii" in exI, simp add: m power_mult)
+      apply (cases "even m", rule_tac x="- ii" in exI, simp add: m power_mult diff_def)
+      apply (rule_tac x="ii" in exI, simp add: m power_mult diff_def)
+      done
+    then obtain v where v: "cmod (complex_of_real (cmod b) / b + v^n) < 1" by blast
+    let ?w = "v / complex_of_real (root n (cmod b))"
+    from odd_real_root_pow[OF o, of "cmod b"]
+    have th1: "?w ^ n = v^n / complex_of_real (cmod b)"
+      by (simp add: power_divide complex_of_real_power)
+    have th2:"cmod (complex_of_real (cmod b) / b) = 1" using b by (simp add: cmod_divide)
+    hence th3: "cmod (complex_of_real (cmod b) / b) \<ge> 0" by simp
+    have th4: "cmod (complex_of_real (cmod b) / b) *
+   cmod (1 + b * (v ^ n / complex_of_real (cmod b)))
+   < cmod (complex_of_real (cmod b) / b) * 1"
+      apply (simp only: cmod_mult[symmetric] right_distrib)
+      using b v by (simp add: th2)
+
+    from mult_less_imp_less_left[OF th4 th3]
+    have "?P ?w n" unfolding th1 .
+    hence "\<exists>z. ?P z n" .. }
+  ultimately show "\<exists>z. ?P z n" by blast
+qed
+
+
+text{* Bolzano-Weierstrass type property for closed disc in complex plane. *}
+
+lemma metric_bound_lemma: "cmod (x - y) <= \<bar>Re x - Re y\<bar> + \<bar>Im x - Im y\<bar>"
+  using real_sqrt_sum_squares_triangle_ineq[of "Re x - Re y" 0 0 "Im x - Im y" ]
+  unfolding cmod_def by simp
+
+lemma bolzano_weierstrass_complex_disc:
+  assumes r: "\<forall>n. cmod (s n) \<le> r"
+  shows "\<exists>f z. subseq f \<and> (\<forall>e >0. \<exists>N. \<forall>n \<ge> N. cmod (s (f n) - z) < e)"
+proof-
+  from seq_monosub[of "Re o s"]
+  obtain f g where f: "subseq f" "monoseq (\<lambda>n. Re (s (f n)))"
+    unfolding o_def by blast
+  from seq_monosub[of "Im o s o f"]
+  obtain g where g: "subseq g" "monoseq (\<lambda>n. Im (s(f(g n))))" unfolding o_def by blast
+  let ?h = "f o g"
+  from r[rule_format, of 0] have rp: "r \<ge> 0" using cmod_pos[of "s 0"] by arith
+  have th:"\<forall>n. r + 1 \<ge> \<bar> Re (s n)\<bar>"
+  proof
+    fix n
+    from abs_Re_le_cmod[of "s n"] r[rule_format, of n]  show "\<bar>Re (s n)\<bar> \<le> r + 1" by arith
+  qed
+  have conv1: "convergent (\<lambda>n. Re (s ( f n)))"
+    apply (rule Bseq_monoseq_convergent)
+    apply (rule exI[where x= "r + 1"])
+    using th rp apply simp
+    using f(2) .
+  have th:"\<forall>n. r + 1 \<ge> \<bar> Im (s n)\<bar>"
+  proof
+    fix n
+    from abs_Im_le_cmod[of "s n"] r[rule_format, of n]  show "\<bar>Im (s n)\<bar> \<le> r + 1" by arith
+  qed
+
+  have conv2: "convergent (\<lambda>n. Im (s (f (g n))))"
+    apply (rule Bseq_monoseq_convergent)
+    apply (rule exI[where x= "r + 1"])
+    using th rp apply simp
+    using g(2) .
+
+  from conv1[unfolded convergent_def] obtain x where "LIMSEQ (\<lambda>n. Re (s (f n))) x"
+    by blast
+  hence  x: "\<forall>r>0. \<exists>n0. \<forall>n\<ge>n0. \<bar> Re (s (f n)) - x \<bar> < r"
+    unfolding LIMSEQ_def real_norm_def .
+
+  from conv2[unfolded convergent_def] obtain y where "LIMSEQ (\<lambda>n. Im (s (f (g n)))) y"
+    by blast
+  hence  y: "\<forall>r>0. \<exists>n0. \<forall>n\<ge>n0. \<bar> Im (s (f (g n))) - y \<bar> < r"
+    unfolding LIMSEQ_def real_norm_def .
+  let ?w = "Complex x y"
+  from f(1) g(1) have hs: "subseq ?h" unfolding subseq_def by auto
+  {fix e assume ep: "e > (0::real)"
+    hence e2: "e/2 > 0" by simp
+    from x[rule_format, OF e2] y[rule_format, OF e2]
+    obtain N1 N2 where N1: "\<forall>n\<ge>N1. \<bar>Re (s (f n)) - x\<bar> < e / 2" and N2: "\<forall>n\<ge>N2. \<bar>Im (s (f (g n))) - y\<bar> < e / 2" by blast
+    {fix n assume nN12: "n \<ge> N1 + N2"
+      hence nN1: "g n \<ge> N1" and nN2: "n \<ge> N2" using seq_suble[OF g(1), of n] by arith+
+      from add_strict_mono[OF N1[rule_format, OF nN1] N2[rule_format, OF nN2]]
+      have "cmod (s (?h n) - ?w) < e"
+	using metric_bound_lemma[of "s (f (g n))" ?w] by simp }
+    hence "\<exists>N. \<forall>n\<ge>N. cmod (s (?h n) - ?w) < e" by blast }
+  with hs show ?thesis  by blast
+qed
+
+text{* Polynomial is continuous. *}
+
+lemma poly_cont:
+  assumes ep: "e > 0"
+  shows "\<exists>d >0. \<forall>w. 0 < cmod (w - z) \<and> cmod (w - z) < d \<longrightarrow> cmod (poly p w - poly p z) < e"
+proof-
+  from poly_offset[of p z] obtain q where q: "length q = length p" "\<And>x. poly q x = poly p (z + x)" by blast
+  {fix w
+    note q(2)[of "w - z", simplified]}
+  note th = this
+  show ?thesis unfolding th[symmetric]
+  proof(induct q)
+    case Nil thus ?case  using ep by auto
+  next
+    case (Cons c cs)
+    from poly_bound_exists[of 1 "cs"]
+    obtain m where m: "m > 0" "\<And>z. cmod z \<le> 1 \<Longrightarrow> cmod (poly cs z) \<le> m" by blast
+    from ep m(1) have em0: "e/m > 0" by (simp add: field_simps)
+    have one0: "1 > (0::real)"  by arith
+    from real_lbound_gt_zero[OF one0 em0]
+    obtain d where d: "d >0" "d < 1" "d < e / m" by blast
+    from d(1,3) m(1) have dm: "d*m > 0" "d*m < e"
+      by (simp_all add: field_simps real_mult_order)
+    show ?case
+      proof(rule ex_forward[OF real_lbound_gt_zero[OF one0 em0]], clarsimp simp add: cmod_mult)
+	fix d w
+	assume H: "d > 0" "d < 1" "d < e/m" "w\<noteq>z" "cmod (w-z) < d"
+	hence d1: "cmod (w-z) \<le> 1" "d \<ge> 0" by simp_all
+	from H(3) m(1) have dme: "d*m < e" by (simp add: field_simps)
+	from H have th: "cmod (w-z) \<le> d" by simp
+	from mult_mono[OF th m(2)[OF d1(1)] d1(2) cmod_pos] dme
+	show "cmod (w - z) * cmod (poly cs (w - z)) < e" by simp
+      qed
+    qed
+qed
+
+text{* Hence a polynomial attains minimum on a closed disc
+  in the complex plane. *}
+lemma  poly_minimum_modulus_disc:
+  "\<exists>z. \<forall>w. cmod w \<le> r \<longrightarrow> cmod (poly p z) \<le> cmod (poly p w)"
+proof-
+  {assume "\<not> r \<ge> 0" hence ?thesis unfolding linorder_not_le
+      apply -
+      apply (rule exI[where x=0])
+      apply auto
+      apply (subgoal_tac "cmod w < 0")
+      apply simp
+      apply arith
+      done }
+  moreover
+  {assume rp: "r \<ge> 0"
+    from rp have "cmod 0 \<le> r \<and> cmod (poly p 0) = - (- cmod (poly p 0))" by simp
+    hence mth1: "\<exists>x z. cmod z \<le> r \<and> cmod (poly p z) = - x"  by blast
+    {fix x z
+      assume H: "cmod z \<le> r" "cmod (poly p z) = - x" "\<not>x < 1"
+      hence "- x < 0 " by arith
+      with H(2) cmod_pos[of "poly p z"]  have False by simp }
+    then have mth2: "\<exists>z. \<forall>x. (\<exists>z. cmod z \<le> r \<and> cmod (poly p z) = - x) \<longrightarrow> x < z" by blast
+    from real_sup_exists[OF mth1 mth2] obtain s where
+      s: "\<forall>y. (\<exists>x. (\<exists>z. cmod z \<le> r \<and> cmod (poly p z) = - x) \<and> y < x) \<longleftrightarrow>(y < s)" by blast
+    let ?m = "-s"
+    {fix y
+      from s[rule_format, of "-y"] have
+    "(\<exists>z x. cmod z \<le> r \<and> -(- cmod (poly p z)) < y) \<longleftrightarrow> ?m < y"
+	unfolding minus_less_iff[of y ] equation_minus_iff by blast }
+    note s1 = this[unfolded minus_minus]
+    from s1[of ?m] have s1m: "\<And>z x. cmod z \<le> r \<Longrightarrow> cmod (poly p z) \<ge> ?m"
+      by auto
+    {fix n::nat
+      from s1[rule_format, of "?m + 1/real (Suc n)"]
+      have "\<exists>z. cmod z \<le> r \<and> cmod (poly p z) < - s + 1 / real (Suc n)"
+	by simp}
+    hence th: "\<forall>n. \<exists>z. cmod z \<le> r \<and> cmod (poly p z) < - s + 1 / real (Suc n)" ..
+    from choice[OF th] obtain g where
+      g: "\<forall>n. cmod (g n) \<le> r" "\<forall>n. cmod (poly p (g n)) <?m+1 /real(Suc n)"
+      by blast
+    from bolzano_weierstrass_complex_disc[OF g(1)]
+    obtain f z where fz: "subseq f" "\<forall>e>0. \<exists>N. \<forall>n\<ge>N. cmod (g (f n) - z) < e"
+      by blast
+    {fix w
+      assume wr: "cmod w \<le> r"
+      let ?e = "\<bar>cmod (poly p z) - ?m\<bar>"
+      {assume e: "?e > 0"
+	hence e2: "?e/2 > 0" by simp
+	from poly_cont[OF e2, of z p] obtain d where
+	  d: "d>0" "\<forall>w. 0<cmod (w - z)\<and> cmod(w - z) < d \<longrightarrow> cmod(poly p w - poly p z) < ?e/2" by blast
+	{fix w assume w: "cmod (w - z) < d"
+	  have "cmod(poly p w - poly p z) < ?e / 2"
+	    using d(2)[rule_format, of w] w e by (cases "w=z", simp_all)}
+	note th1 = this
+
+	from fz(2)[rule_format, OF d(1)] obtain N1 where
+	  N1: "\<forall>n\<ge>N1. cmod (g (f n) - z) < d" by blast
+	from reals_Archimedean2[of "2/?e"] obtain N2::nat where
+	  N2: "2/?e < real N2" by blast
+	have th2: "cmod(poly p (g(f(N1 + N2))) - poly p z) < ?e/2"
+	  using N1[rule_format, of "N1 + N2"] th1 by simp
+	{fix a b e2 m :: real
+	have "a < e2 \<Longrightarrow> abs(b - m) < e2 \<Longrightarrow> 2 * e2 <= abs(b - m) + a
+          ==> False" by arith}
+      note th0 = this
+      have ath:
+	"\<And>m x e. m <= x \<Longrightarrow>  x < m + e ==> abs(x - m::real) < e" by arith
+      from s1m[OF g(1)[rule_format]]
+      have th31: "?m \<le> cmod(poly p (g (f (N1 + N2))))" .
+      from seq_suble[OF fz(1), of "N1+N2"]
+      have th00: "real (Suc (N1+N2)) \<le> real (Suc (f (N1+N2)))" by simp
+      have th000: "0 \<le> (1::real)" "(1::real) \<le> 1" "real (Suc (N1+N2)) > 0"
+	using N2 by auto
+      from frac_le[OF th000 th00] have th00: "?m +1 / real (Suc (f (N1 + N2))) \<le> ?m + 1 / real (Suc (N1 + N2))" by simp
+      from g(2)[rule_format, of "f (N1 + N2)"]
+      have th01:"cmod (poly p (g (f (N1 + N2)))) < - s + 1 / real (Suc (f (N1 + N2)))" .
+      from order_less_le_trans[OF th01 th00]
+      have th32: "cmod(poly p (g (f (N1 + N2)))) < ?m + (1/ real(Suc (N1 + N2)))" .
+      from N2 have "2/?e < real (Suc (N1 + N2))" by arith
+      with e2 less_imp_inverse_less[of "2/?e" "real (Suc (N1 + N2))"]
+      have "?e/2 > 1/ real (Suc (N1 + N2))" by (simp add: inverse_eq_divide)
+      with ath[OF th31 th32]
+      have thc1:"\<bar>cmod(poly p (g (f (N1 + N2)))) - ?m\<bar>< ?e/2" by arith
+      have ath2: "\<And>(a::real) b c m. \<bar>a - b\<bar> <= c ==> \<bar>b - m\<bar> <= \<bar>a - m\<bar> + c"
+	by arith
+      have th22: "\<bar>cmod (poly p (g (f (N1 + N2)))) - cmod (poly p z)\<bar>
+\<le> cmod (poly p (g (f (N1 + N2))) - poly p z)"
+      from ath2[OF th22, of ?m]
+      have thc2: "2*(?e/2) \<le> \<bar>cmod(poly p (g (f (N1 + N2)))) - ?m\<bar> + cmod (poly p (g (f (N1 + N2))) - poly p z)" by simp
+      from th0[OF th2 thc1 thc2] have False .}
+      hence "?e = 0" by auto
+      then have "cmod (poly p z) = ?m" by simp
+      with s1m[OF wr]
+      have "cmod (poly p z) \<le> cmod (poly p w)" by simp }
+    hence ?thesis by blast}
+  ultimately show ?thesis by blast
+qed
+
+lemma "(rcis (sqrt (abs r)) (a/2)) ^ 2 = rcis (abs r) a"
+  unfolding power2_eq_square
+  done
+
+lemma cispi: "cis pi = -1"
+  unfolding cis_def
+  by simp
+
+lemma "(rcis (sqrt (abs r)) ((pi + a)/2)) ^ 2 = rcis (- abs r) a"
+  unfolding power2_eq_square
+  apply (simp add: power2_eq_square[symmetric] rcis_def cispi cis_mult[symmetric])
+  done
+
+text {* Nonzero polynomial in z goes to infinity as z does. *}
+
+instance complex::idom_char_0 by (intro_classes)
+instance complex :: recpower_idom_char_0 by intro_classes
+
+lemma poly_infinity:
+  assumes ex: "list_ex (\<lambda>c. c \<noteq> 0) p"
+  shows "\<exists>r. \<forall>z. r \<le> cmod z \<longrightarrow> d \<le> cmod (poly (a#p) z)"
+using ex
+proof(induct p arbitrary: a d)
+  case (Cons c cs a d)
+  {assume H: "list_ex (\<lambda>c. c\<noteq>0) cs"
+    with Cons.hyps obtain r where r: "\<forall>z. r \<le> cmod z \<longrightarrow> d + cmod a \<le> cmod (poly (c # cs) z)" by blast
+    let ?r = "1 + \<bar>r\<bar>"
+    {fix z assume h: "1 + \<bar>r\<bar> \<le> cmod z"
+      have r0: "r \<le> cmod z" using h by arith
+      from r[rule_format, OF r0]
+      have th0: "d + cmod a \<le> 1 * cmod(poly (c#cs) z)" by arith
+      from h have z1: "cmod z \<ge> 1" by arith
+      from order_trans[OF th0 mult_right_mono[OF z1 cmod_pos[of "poly (c#cs) z"]]]
+      have th1: "d \<le> cmod(z * poly (c#cs) z) - cmod a"
+	unfolding cmod_mult by (simp add: ring_simps)
+      from complex_mod_triangle_sub[of "z * poly (c#cs) z" a]
+      have th2: "cmod(z * poly (c#cs) z) - cmod a \<le> cmod (poly (a#c#cs) z)"
+	by (simp add: diff_le_eq ring_simps)
+      from th1 th2 have "d \<le> cmod (poly (a#c#cs) z)"  by arith}
+    hence ?case by blast}
+  moreover
+  {assume cs0: "\<not> (list_ex (\<lambda>c. c \<noteq> 0) cs)"
+    with Cons.prems have c0: "c \<noteq> 0" by simp
+    from cs0 have cs0': "list_all (\<lambda>c. c = 0) cs"
+      by (auto simp add: list_all_iff list_ex_iff)
+    {fix z
+      assume h: "(\<bar>d\<bar> + cmod a) / cmod c \<le> cmod z"
+      from c0 have "cmod c > 0" by simp
+      from h c0 have th0: "\<bar>d\<bar> + cmod a \<le> cmod (z*c)"
+	by (simp add: field_simps cmod_mult)
+      have ath: "\<And>mzh mazh ma. mzh <= mazh + ma ==> abs(d) + ma <= mzh ==> d <= mazh" by arith
+      from complex_mod_triangle_sub[of "z*c" a ]
+      have th1: "cmod (z * c) \<le> cmod (a + z * c) + cmod a"
+      from ath[OF th1 th0] have "d \<le> cmod (poly (a # c # cs) z)"
+	using poly_0[OF cs0'] by simp}
+    then have ?case  by blast}
+  ultimately show ?case by blast
+qed simp
+
+text {* Hence polynomial's modulus attains its minimum somewhere. *}
+lemma poly_minimum_modulus:
+  "\<exists>z.\<forall>w. cmod (poly p z) \<le> cmod (poly p w)"
+proof(induct p)
+  case (Cons c cs)
+  {assume cs0: "list_ex (\<lambda>c. c \<noteq> 0) cs"
+    from poly_infinity[OF cs0, of "cmod (poly (c#cs) 0)" c]
+    obtain r where r: "\<And>z. r \<le> cmod z \<Longrightarrow> cmod (poly (c # cs) 0) \<le> cmod (poly (c # cs) z)" by blast
+    have ath: "\<And>z r. r \<le> cmod z \<or> cmod z \<le> \<bar>r\<bar>" by arith
+    from poly_minimum_modulus_disc[of "\<bar>r\<bar>" "c#cs"]
+    obtain v where v: "\<And>w. cmod w \<le> \<bar>r\<bar> \<Longrightarrow> cmod (poly (c # cs) v) \<le> cmod (poly (c # cs) w)" by blast
+    {fix z assume z: "r \<le> cmod z"
+      from v[of 0] r[OF z]
+      have "cmod (poly (c # cs) v) \<le> cmod (poly (c # cs) z)"
+	by simp }
+    note v0 = this
+    from v0 v ath[of r] have ?case by blast}
+  moreover
+  {assume cs0: "\<not> (list_ex (\<lambda>c. c\<noteq>0) cs)"
+    hence th:"list_all (\<lambda>c. c = 0) cs" by (simp add: list_all_iff list_ex_iff)
+    from poly_0[OF th] Cons.hyps have ?case by simp}
+  ultimately show ?case by blast
+qed simp
+
+text{* Constant function (non-syntactic characterization). *}
+definition "constant f = (\<forall>x y. f x = f y)"
+
+lemma nonconstant_length: "\<not> (constant (poly p)) \<Longrightarrow> length p \<ge> 2"
+  unfolding constant_def
+  apply (induct p, auto)
+  apply (unfold not_less[symmetric])
+  apply simp
+  apply (rule ccontr)
+  apply auto
+  done
+
+lemma poly_replicate_append:
+  "poly ((replicate n 0)@p) (x::'a::{recpower, comm_ring}) = x^n * poly p x"
+  by(induct n, auto simp add: power_Suc ring_simps)
+
+text {* Decomposition of polynomial, skipping zero coefficients
+  after the first.  *}
+
+lemma poly_decompose_lemma:
+ assumes nz: "\<not>(\<forall>z. z\<noteq>0 \<longrightarrow> poly p z = (0::'a::{recpower,idom}))"
+  shows "\<exists>k a q. a\<noteq>0 \<and> Suc (length q + k) = length p \<and>
+                 (\<forall>z. poly p z = z^k * poly (a#q) z)"
+using nz
+proof(induct p)
+  case Nil thus ?case by simp
+next
+  case (Cons c cs)
+  {assume c0: "c = 0"
+
+    from Cons.hyps Cons.prems c0 have ?case apply auto
+      apply (rule_tac x="k+1" in exI)
+      apply (rule_tac x="a" in exI, clarsimp)
+      apply (rule_tac x="q" in exI)
+      by (auto simp add: power_Suc)}
+  moreover
+  {assume c0: "c\<noteq>0"
+    hence ?case apply-
+      apply (rule exI[where x=0])
+      apply (rule exI[where x=c], clarsimp)
+      apply (rule exI[where x=cs])
+      apply auto
+      done}
+  ultimately show ?case by blast
+qed
+
+lemma poly_decompose:
+  assumes nc: "~constant(poly p)"
+  shows "\<exists>k a q. a\<noteq>(0::'a::{recpower,idom}) \<and> k\<noteq>0 \<and>
+               length q + k + 1 = length p \<and>
+              (\<forall>z. poly p z = poly p 0 + z^k * poly (a#q) z)"
+using nc
+proof(induct p)
+  case Nil thus ?case by (simp add: constant_def)
+next
+  case (Cons c cs)
+  {assume C:"\<forall>z. z \<noteq> 0 \<longrightarrow> poly cs z = 0"
+    {fix x y
+      from C have "poly (c#cs) x = poly (c#cs) y" by (cases "x=0", auto)}
+    with Cons.prems have False by (auto simp add: constant_def)}
+  hence th: "\<not> (\<forall>z. z \<noteq> 0 \<longrightarrow> poly cs z = 0)" ..
+  from poly_decompose_lemma[OF th]
+  show ?case
+    apply clarsimp
+    apply (rule_tac x="k+1" in exI)
+    apply (rule_tac x="a" in exI)
+    apply simp
+    apply (rule_tac x="q" in exI)
+    apply (auto simp add: power_Suc)
+    done
+qed
+
+text{* Fundamental theorem of algebral *}
+
+lemma fundamental_theorem_of_algebra:
+  assumes nc: "~constant(poly p)"
+  shows "\<exists>z::complex. poly p z = 0"
+using nc
+proof(induct n\<equiv> "length p" arbitrary: p rule: nat_less_induct)
+  fix n fix p :: "complex list"
+  let ?p = "poly p"
+  assume H: "\<forall>m<n. \<forall>p. \<not> constant (poly p) \<longrightarrow> m = length p \<longrightarrow> (\<exists>(z::complex). poly p z = 0)" and nc: "\<not> constant ?p" and n: "n = length p"
+  let ?ths = "\<exists>z. ?p z = 0"
+
+  from nonconstant_length[OF nc] have n2: "n\<ge> 2" by (simp add: n)
+  from poly_minimum_modulus obtain c where
+    c: "\<forall>w. cmod (?p c) \<le> cmod (?p w)" by blast
+  {assume pc: "?p c = 0" hence ?ths by blast}
+  moreover
+  {assume pc0: "?p c \<noteq> 0"
+    from poly_offset[of p c] obtain q where
+      q: "length q = length p" "\<forall>x. poly q x = ?p (c+x)" by blast
+    {assume h: "constant (poly q)"
+      from q(2) have th: "\<forall>x. poly q (x - c) = ?p x" by auto
+      {fix x y
+	from th have "?p x = poly q (x - c)" by auto
+	also have "\<dots> = poly q (y - c)"
+	  using h unfolding constant_def by blast
+	also have "\<dots> = ?p y" using th by auto
+	finally have "?p x = ?p y" .}
+      with nc have False unfolding constant_def by blast }
+    hence qnc: "\<not> constant (poly q)" by blast
+    from q(2) have pqc0: "?p c = poly q 0" by simp
+    from c pqc0 have cq0: "\<forall>w. cmod (poly q 0) \<le> cmod (?p w)" by simp
+    let ?a0 = "poly q 0"
+    from pc0 pqc0 have a00: "?a0 \<noteq> 0" by simp
+    from a00
+    have qr: "\<forall>z. poly q z = poly (map (op * (inverse ?a0)) q) z * ?a0"
+    let ?r = "map (op * (inverse ?a0)) q"
+    have lgqr: "length q = length ?r" by simp
+    {assume h: "\<And>x y. poly ?r x = poly ?r y"
+      {fix x y
+	from qr[rule_format, of x]
+	have "poly q x = poly ?r x * ?a0" by auto
+	also have "\<dots> = poly ?r y * ?a0" using h by simp
+	also have "\<dots> = poly q y" using qr[rule_format, of y] by simp
+	finally have "poly q x = poly q y" .}
+      with qnc have False unfolding constant_def by blast}
+    hence rnc: "\<not> constant (poly ?r)" unfolding constant_def by blast
+    from qr[rule_format, of 0] a00  have r01: "poly ?r 0 = 1" by auto
+    {fix w
+      have "cmod (poly ?r w) < 1 \<longleftrightarrow> cmod (poly q w / ?a0) < 1"
+	using qr[rule_format, of w] a00 by simp
+      also have "\<dots> \<longleftrightarrow> cmod (poly q w) < cmod ?a0"
+	using a00 unfolding cmod_divide by (simp add: field_simps)
+      finally have "cmod (poly ?r w) < 1 \<longleftrightarrow> cmod (poly q w) < cmod ?a0" .}
+    note mrmq_eq = this
+    from poly_decompose[OF rnc] obtain k a s where
+      kas: "a\<noteq>0" "k\<noteq>0" "length s + k + 1 = length ?r"
+      "\<forall>z. poly ?r z = poly ?r 0 + z^k* poly (a#s) z" by blast
+    {assume "k + 1 = n"
+      with kas(3) lgqr[symmetric] q(1) n[symmetric] have s0:"s=[]" by auto
+      {fix w
+	have "cmod (poly ?r w) = cmod (1 + a * w ^ k)"
+	  using kas(4)[rule_format, of w] s0 r01 by (simp add: ring_simps)}
+      note hth = this [symmetric]
+	from reduce_poly_simple[OF kas(1,2)]
+      have "\<exists>w. cmod (poly ?r w) < 1" unfolding hth by blast}
+    moreover
+    {assume kn: "k+1 \<noteq> n"
+      from kn kas(3) q(1) n[symmetric] have k1n: "k + 1 < n" by simp
+      have th01: "\<not> constant (poly (1#((replicate (k - 1) 0)@[a])))"
+	unfolding constant_def poly_Nil poly_Cons poly_replicate_append
+	using kas(1) apply simp
+	by (rule exI[where x=0], rule exI[where x=1], simp)
+      from kas(2) have th02: "k+1 = length (1#((replicate (k - 1) 0)@[a]))"
+	by simp
+      from H[rule_format, OF k1n th01 th02]
+      obtain w where w: "1 + w^k * a = 0"
+	unfolding poly_Nil poly_Cons poly_replicate_append
+	using kas(2) by (auto simp add: power_Suc[symmetric, of _ "k - Suc 0"]
+	  mult_assoc[of _ _ a, symmetric])
+      from poly_bound_exists[of "cmod w" s] obtain m where
+	m: "m > 0" "\<forall>z. cmod z \<le> cmod w \<longrightarrow> cmod (poly s z) \<le> m" by blast
+      have w0: "w\<noteq>0" using kas(2) w by (auto simp add: power_0_left)
+      from w have "(1 + w ^ k * a) - 1 = 0 - 1" by simp
+      then have wm1: "w^k * a = - 1" by simp
+      have inv0: "0 < inverse (cmod w ^ (k + 1) * m)"
+	using cmod_pos[of w] w0 m(1)
+	  by (simp add: inverse_eq_divide zero_less_mult_iff)
+      with real_down2[OF zero_less_one] obtain t where
+	t: "t > 0" "t < 1" "t < inverse (cmod w ^ (k + 1) * m)" by blast
+      let ?ct = "complex_of_real t"
+      let ?w = "?ct * w"
+      have "1 + ?w^k * (a + ?w * poly s ?w) = 1 + ?ct^k * (w^k * a) + ?w^k * ?w * poly s ?w" using kas(1) by (simp add: ring_simps power_mult_distrib)
+      also have "\<dots> = complex_of_real (1 - t^k) + ?w^k * ?w * poly s ?w"
+	unfolding wm1 by (simp)
+      finally have "cmod (1 + ?w^k * (a + ?w * poly s ?w)) = cmod (complex_of_real (1 - t^k) + ?w^k * ?w * poly s ?w)"
+	apply -
+	apply (rule cong[OF refl[of cmod]])
+	apply assumption
+	done
+      with complex_mod_triangle_ineq[of "complex_of_real (1 - t^k)" "?w^k * ?w * poly s ?w"]
+      have th11: "cmod (1 + ?w^k * (a + ?w * poly s ?w)) \<le> \<bar>1 - t^k\<bar> + cmod (?w^k * ?w * poly s ?w)" unfolding cmod_complex_of_real by simp
+      have ath: "\<And>x (t::real). 0\<le> x \<Longrightarrow> x < t \<Longrightarrow> t\<le>1 \<Longrightarrow> \<bar>1 - t\<bar> + x < 1" by arith
+      have "t *cmod w \<le> 1 * cmod w" apply (rule mult_mono) using t(1,2) by auto
+      then have tw: "cmod ?w \<le> cmod w" using t(1) by (simp add: cmod_mult)
+      from t inv0 have "t* (cmod w ^ (k + 1) * m) < 1"
+	by (simp add: inverse_eq_divide field_simps)
+      with zero_less_power[OF t(1), of k]
+      have th30: "t^k * (t* (cmod w ^ (k + 1) * m)) < t^k * 1"
+	apply - apply (rule mult_strict_left_mono) by simp_all
+      have "cmod (?w^k * ?w * poly s ?w) = t^k * (t* (cmod w ^ (k+1) * cmod (poly s ?w)))"  using w0 t(1)
+	by (simp add: ring_simps power_mult_distrib cmod_complex_of_real cmod_power cmod_mult)
+      then have "cmod (?w^k * ?w * poly s ?w) \<le> t^k * (t* (cmod w ^ (k + 1) * m))"
+	using t(1,2) m(2)[rule_format, OF tw] w0
+	apply (simp only: )
+	apply auto
+	apply (rule mult_mono, simp_all add: cmod_pos)+
+	apply (simp add: zero_le_mult_iff zero_le_power)
+	done
+      with th30 have th120: "cmod (?w^k * ?w * poly s ?w) < t^k" by simp
+      from power_strict_mono[OF t(2), of k] t(1) kas(2) have th121: "t^k \<le> 1"
+	by auto
+      from ath[OF cmod_pos[of "?w^k * ?w * poly s ?w"] th120 th121]
+      have th12: "\<bar>1 - t^k\<bar> + cmod (?w^k * ?w * poly s ?w) < 1" .
+      from th11 th12
+      have "cmod (1 + ?w^k * (a + ?w * poly s ?w)) < 1"  by arith
+      then have "cmod (poly ?r ?w) < 1"
+	unfolding kas(4)[rule_format, of ?w] r01 by simp
+      then have "\<exists>w. cmod (poly ?r w) < 1" by blast}
+    ultimately have cr0_contr: "\<exists>w. cmod (poly ?r w) < 1" by blast
+    from cr0_contr cq0 q(2)
+    have ?ths unfolding mrmq_eq not_less[symmetric] by auto}
+  ultimately show ?ths by blast
+qed
+
+text {* Alternative version with a syntactic notion of constant polynomial. *}
+
+lemma fundamental_theorem_of_algebra_alt:
+  assumes nc: "~(\<exists>a l. a\<noteq> 0 \<and> list_all(\<lambda>b. b = 0) l \<and> p = a#l)"
+  shows "\<exists>z. poly p z = (0::complex)"
+using nc
+proof(induct p)
+  case (Cons c cs)
+  {assume "c=0" hence ?case by auto}
+  moreover
+  {assume c0: "c\<noteq>0"
+    {assume nc: "constant (poly (c#cs))"
+      from nc[unfolded constant_def, rule_format, of 0]
+      have "\<forall>w. w \<noteq> 0 \<longrightarrow> poly cs w = 0" by auto
+      hence "list_all (\<lambda>c. c=0) cs"
+	proof(induct cs)
+	  case (Cons d ds)
+	  {assume "d=0" hence ?case using Cons.prems Cons.hyps by simp}
+	  moreover
+	  {assume d0: "d\<noteq>0"
+	    from poly_bound_exists[of 1 ds] obtain m where
+	      m: "m > 0" "\<forall>z. \<forall>z. cmod z \<le> 1 \<longrightarrow> cmod (poly ds z) \<le> m" by blast
+	    have dm: "cmod d / m > 0" using d0 m(1) by (simp add: field_simps)
+	    from real_down2[OF dm zero_less_one] obtain x where
+	      x: "x > 0" "x < cmod d / m" "x < 1" by blast
+	    let ?x = "complex_of_real x"
+	    from x have cx: "?x \<noteq> 0"  "cmod ?x \<le> 1" by simp_all
+	    from Cons.prems[rule_format, OF cx(1)]
+	    have cth: "cmod (?x*poly ds ?x) = cmod d" by (simp add: eq_diff_eq[symmetric])
+	    from m(2)[rule_format, OF cx(2)] x(1)
+	    have th0: "cmod (?x*poly ds ?x) \<le> x*m"
+	    from x(2) m(1) have "x*m < cmod d" by (simp add: field_simps)
+	    with th0 have "cmod (?x*poly ds ?x) \<noteq> cmod d" by auto
+	    with cth  have ?case by blast}
+	  ultimately show ?case by blast
+	qed simp}
+      then have nc: "\<not> constant (poly (c#cs))" using Cons.prems c0
+	by blast
+      from fundamental_theorem_of_algebra[OF nc] have ?case .}
+  ultimately show ?case by blast
+qed simp
+
+section{* Nullstellenstatz, degrees and divisibility of polynomials *}
+
+lemma nullstellensatz_lemma:
+  fixes p :: "complex list"
+  assumes "\<forall>x. poly p x = 0 \<longrightarrow> poly q x = 0"
+  and "degree p = n" and "n \<noteq> 0"
+  shows "p divides (pexp q n)"
+using prems
+proof(induct n arbitrary: p q rule: nat_less_induct)
+  fix n::nat fix p q :: "complex list"
+  assume IH: "\<forall>m<n. \<forall>p q.
+                 (\<forall>x. poly p x = (0::complex) \<longrightarrow> poly q x = 0) \<longrightarrow>
+                 degree p = m \<longrightarrow> m \<noteq> 0 \<longrightarrow> p divides (q %^ m)"
+    and pq0: "\<forall>x. poly p x = 0 \<longrightarrow> poly q x = 0"
+    and dpn: "degree p = n" and n0: "n \<noteq> 0"
+  let ?ths = "p divides (q %^ n)"
+  {fix a assume a: "poly p a = 0"
+    {assume p0: "poly p = poly []"
+      hence ?ths unfolding divides_def  using pq0 n0
+	apply - apply (rule exI[where x="[]"], rule ext)
+	by (auto simp add: poly_mult poly_exp)}
+    moreover
+    {assume p0: "poly p \<noteq> poly []"
+      and oa: "order  a p \<noteq> 0"
+      from p0 have pne: "p \<noteq> []" by auto
+      let ?op = "order a p"
+      from p0 have ap: "([- a, 1] %^ ?op) divides p"
+	"\<not> pexp [- a, 1] (Suc ?op) divides p" using order by blast+
+      note oop = order_degree[OF p0, unfolded dpn]
+      {assume q0: "q = []"
+	hence ?ths using n0 unfolding divides_def
+	  apply simp
+	  apply (rule exI[where x="[]"], rule ext)
+	  by (simp add: divides_def poly_exp poly_mult)}
+      moreover
+      {assume q0: "q\<noteq>[]"
+	from pq0[rule_format, OF a, unfolded poly_linear_divides] q0
+	obtain r where r: "q = pmult [- a, 1] r" by blast
+	from ap[unfolded divides_def] obtain s where
+	  s: "poly p = poly (pmult (pexp [- a, 1] ?op) s)" by blast
+	have s0: "poly s \<noteq> poly []"
+	  using s p0 by (simp add: poly_entire)
+	hence pns0: "poly (pnormalize s) \<noteq> poly []" and sne: "s\<noteq>[]" by auto
+	{assume ds0: "degree s = 0"
+	  from ds0 pns0 have "\<exists>k. pnormalize s = [k]" unfolding degree_def
+	    by (cases "pnormalize s", auto)
+	  then obtain k where kpn: "pnormalize s = [k]" by blast
+	  from pns0[unfolded poly_zero] kpn have k: "k \<noteq>0" "poly s = poly [k]"
+	    using poly_normalize[of s] by simp_all
+	  let ?w = "pmult (pmult [1/k] (pexp [-a,1] (n - ?op))) (pexp r n)"
+	  from k r s oop have "poly (pexp q n) = poly (pmult p ?w)"
+	  hence ?ths unfolding divides_def by blast}
+	moreover
+	{assume ds0: "degree s \<noteq> 0"
+	  from ds0 s0 dpn degree_unique[OF s, unfolded linear_pow_mul_degree] oa
+	    have dsn: "degree s < n" by auto
+	    {fix x assume h: "poly s x = 0"
+	      {assume xa: "x = a"
+		from h[unfolded xa poly_linear_divides] sne obtain u where
+		  u: "s = pmult [- a, 1] u" by blast
+		have "poly p = poly (pmult (pexp [- a, 1] (Suc ?op)) u)"
+		  unfolding s u
+		  apply (rule ext)
+		with ap(2)[unfolded divides_def] have False by blast}
+	      note xa = this
+	      from h s have "poly p x = 0" by (simp add: poly_mult)
+	      with pq0 have "poly q x = 0" by blast
+	      with r xa have "poly r x = 0"
+	    note impth = this
+	    from IH[rule_format, OF dsn, of s r] impth ds0
+	    have "s divides (pexp r (degree s))" by blast
+	    then obtain u where u: "poly (pexp r (degree s)) = poly (pmult s u)"
+	      unfolding divides_def by blast
+	    hence u': "\<And>x. poly s x * poly u x = poly r x ^ degree s"
+	      by (simp add: poly_mult[symmetric] poly_exp[symmetric])
+	    let ?w = "pmult (pmult u (pexp [-a,1] (n - ?op))) (pexp r (n - degree s))"
+	    from u' s r oop[of a] dsn have "poly (pexp q n) = poly (pmult p ?w)"
+	      apply - apply (rule ext)
+
+	      done
+	    hence ?ths unfolding divides_def by blast}
+      ultimately have ?ths by blast }
+      ultimately have ?ths by blast}
+    ultimately have ?ths using a order_root by blast}
+  moreover
+  {assume exa: "\<not> (\<exists>a. poly p a = 0)"
+    from fundamental_theorem_of_algebra_alt[of p] exa obtain c cs where
+      ccs: "c\<noteq>0" "list_all (\<lambda>c. c = 0) cs" "p = c#cs" by blast
+
+    from poly_0[OF ccs(2)] ccs(3)
+    have pp: "\<And>x. poly p x =  c" by simp
+    let ?w = "pmult [1/c] (pexp q n)"
+    from pp ccs(1)
+    have "poly (pexp q n) = poly (pmult p ?w) "
+      apply - apply (rule ext)
+      unfolding poly_mult_assoc[symmetric] by (simp add: poly_mult)
+    hence ?ths unfolding divides_def by blast}
+  ultimately show ?ths by blast
+qed
+
+lemma nullstellensatz_univariate:
+  "(\<forall>x. poly p x = (0::complex) \<longrightarrow> poly q x = 0) \<longleftrightarrow>
+    p divides (q %^ (degree p)) \<or> (poly p = poly [] \<and> poly q = poly [])"
+proof-
+  {assume pe: "poly p = poly []"
+    hence eq: "(\<forall>x. poly p x = (0::complex) \<longrightarrow> poly q x = 0) \<longleftrightarrow> poly q = poly []"
+      apply auto
+      by (rule ext, simp)
+    {assume "p divides (pexp q (degree p))"
+      then obtain r where r: "poly (pexp q (degree p)) = poly (pmult p r)"
+	unfolding divides_def by blast
+      from cong[OF r refl] pe degree_unique[OF pe]
+      have False by (simp add: poly_mult degree_def)}
+    with eq pe have ?thesis by blast}
+  moreover
+  {assume pe: "poly p \<noteq> poly []"
+    have p0: "poly  = poly []" by (rule ext, simp)
+    {assume dp: "degree p = 0"
+      then obtain k where "pnormalize p = [k]" using pe poly_normalize[of p]
+	unfolding degree_def by (cases "pnormalize p", auto)
+      hence k: "pnormalize p = [k]" "poly p = poly [k]" "k\<noteq>0"
+	using pe poly_normalize[of p] by (auto simp add: p0)
+      hence th1: "\<forall>x. poly p x \<noteq> 0" by simp
+      from k(2,3) dp have "poly (pexp q (degree p)) = poly (pmult p [1/k]) "
+	by - (rule ext, simp add: poly_mult poly_exp)
+      hence th2: "p divides (pexp q (degree p))" unfolding divides_def by blast
+      from th1 th2 pe have ?thesis by blast}
+    moreover
+    {assume dp: "degree p \<noteq> 0"
+      then obtain n where n: "degree p = Suc n " by (cases "degree p", auto)
+      {assume "p divides (pexp q (Suc n))"
+	then obtain u where u: "poly (pexp q (Suc n)) = poly (pmult p u)"
+	  unfolding divides_def by blast
+	hence u' :"\<And>x. poly (pexp q (Suc n)) x = poly (pmult p u) x" by simp_all
+	{fix x assume h: "poly p x = 0" "poly q x \<noteq> 0"
+	  hence "poly (pexp q (Suc n)) x \<noteq> 0" by (simp only: poly_exp) simp
+	  hence False using u' h(1) by (simp only: poly_mult poly_exp) simp}}
+	with n nullstellensatz_lemma[of p q "degree p"] dp
+	have ?thesis by auto}
+    ultimately have ?thesis by blast}
+  ultimately show ?thesis by blast
+qed
+
+text{* Useful lemma *}
+
+lemma (in idom_char_0) constant_degree: "constant (poly p) \<longleftrightarrow> degree p = 0" (is "?lhs = ?rhs")
+proof
+  assume l: ?lhs
+  from l[unfolded constant_def, rule_format, of _ "zero"]
+  have th: "poly p = poly [poly p 0]" apply - by (rule ext, simp)
+  from degree_unique[OF th] show ?rhs by (simp add: degree_def)
+next
+  assume r: ?rhs
+  from r have "pnormalize p = [] \<or> (\<exists>k. pnormalize p = [k])"
+    unfolding degree_def by (cases "pnormalize p", auto)
+  then show ?lhs unfolding constant_def poly_normalize[of p, symmetric]
+    by (auto simp del: poly_normalize)
+qed
+
+(* It would be nicer to prove this without using algebraic closure...        *)
+
+lemma divides_degree_lemma: assumes dpn: "degree (p::complex list) = n"
+  shows "n \<le> degree (p *** q) \<or> poly (p *** q) = poly []"
+  using dpn
+proof(induct n arbitrary: p q)
+  case 0 thus ?case by simp
+next
+  case (Suc n p q)
+  from Suc.prems fundamental_theorem_of_algebra[of p] constant_degree[of p]
+  obtain a where a: "poly p a = 0" by auto
+  then obtain r where r: "p = pmult [-a, 1] r" unfolding poly_linear_divides
+    using Suc.prems by (auto simp add: degree_def)
+  {assume h: "poly (pmult r q) = poly []"
+    hence "poly (pmult p q) = poly []" using r
+      apply - apply (rule ext)  by (auto simp add: poly_entire poly_mult poly_add poly_cmult) hence ?case by blast}
+  moreover
+  {assume h: "poly (pmult r q) \<noteq> poly []"
+    hence r0: "poly r \<noteq> poly []" and q0: "poly q \<noteq> poly []"
+      by (auto simp add: poly_entire)
+    have eq: "poly (pmult p q) = poly (pmult [-a, 1] (pmult r q))"
+      apply - apply (rule ext)
+    from linear_mul_degree[OF h, of "- a"]
+    have dqe: "degree (pmult p q) = degree (pmult r q) + 1"
+      unfolding degree_unique[OF eq] .
+    from linear_mul_degree[OF r0, of "- a", unfolded r[symmetric]] r Suc.prems
+    have dr: "degree r = n" by auto
+    from  Suc.hyps[OF dr, of q] have "Suc n \<le> degree (pmult p q)"
+      unfolding dqe using h by (auto simp del: poly.simps)
+    hence ?case by blast}
+  ultimately show ?case by blast
+qed
+
+lemma divides_degree: assumes pq: "p divides (q:: complex list)"
+  shows "degree p \<le> degree q \<or> poly q = poly []"
+using pq  divides_degree_lemma[OF refl, of p]
+apply (auto simp add: divides_def poly_entire)
+apply atomize
+apply (erule_tac x="qa" in allE, auto)
+apply (subgoal_tac "degree q = degree (p *** qa)", simp)
+apply (rule degree_unique, simp)
+done
+
+(* Arithmetic operations on multivariate polynomials.                        *)
+
+lemma mpoly_base_conv:
+  "(0::complex) \<equiv> poly [] x" "c \<equiv> poly [c] x" "x \<equiv> poly [0,1] x" by simp_all
+
+lemma mpoly_norm_conv:
+  "poly  (x::complex) \<equiv> poly [] x" "poly [poly [] y] x \<equiv> poly [] x" by simp_all
+
+lemma mpoly_sub_conv:
+  "poly p (x::complex) - poly q x \<equiv> poly p x + -1 * poly q x"
+
+lemma poly_pad_rule: "poly p x = 0 ==> poly (0#p) x = (0::complex)" by simp
+
+lemma poly_cancel_eq_conv: "p = (0::complex) \<Longrightarrow> a \<noteq> 0 \<Longrightarrow> (q = 0) \<equiv> (a * q - b * p = 0)" apply (atomize (full)) by auto
+
+lemma resolve_eq_raw:  "poly [] x \<equiv> 0" "poly [c] x \<equiv> (c::complex)" by auto
+lemma  resolve_eq_then: "(P \<Longrightarrow> (Q \<equiv> Q1)) \<Longrightarrow> (\<not>P \<Longrightarrow> (Q \<equiv> Q2))
+  \<Longrightarrow> Q \<equiv> P \<and> Q1 \<or> \<not>P\<and> Q2" apply (atomize (full)) by blast
+lemma expand_ex_beta_conv: "list_ex P [c] \<equiv> P c" by simp
+
+  fixes p q :: "complex list"
+  assumes pq: "p divides q"
+  shows "p divides ((0::complex)#q)"
+proof-
+  from pq obtain r where r: "poly q = poly (p *** r)" unfolding divides_def by blast
+  hence "poly (0#q) = poly (p *** ([0,1] *** r))"
+  thus ?thesis unfolding divides_def by blast
+qed
+
+  fixes p q :: "complex list"
+  assumes pq: "p divides q"
+  shows "p divides (a %* q)"
+proof-
+  from pq obtain r where r: "poly q = poly (p *** r)" unfolding divides_def by blast
+  hence "poly (a %* q) = poly (p *** (a %* r))"
+  thus ?thesis unfolding divides_def by blast
+qed
+
+
+lemma poly_divides_conv0:
+  fixes p :: "complex list"
+  assumes lgpq: "length q < length p" and lq:"last p \<noteq> 0"
+  shows "p divides q \<equiv> (\<not> (list_ex (\<lambda>c. c \<noteq> 0) q))" (is "?lhs \<equiv> ?rhs")
+proof-
+  {assume r: ?rhs
+    hence eq: "poly q = poly []" unfolding poly_zero
+      by (simp add: list_all_iff list_ex_iff)
+    hence "poly q = poly (p *** [])" by - (rule ext, simp add: poly_mult)
+    hence ?lhs unfolding divides_def  by blast}
+  moreover
+  {assume l: ?lhs
+    have ath: "\<And>lq lp dq::nat. lq < lp ==> lq \<noteq> 0 \<Longrightarrow> dq <= lq - 1 ==> dq < lp - 1"
+      by arith
+    {assume q0: "length q = 0"
+      hence "q = []" by simp
+      hence ?rhs by simp}
+    moreover
+    {assume lgq0: "length q \<noteq> 0"
+      from pnormalize_length[of q] have dql: "degree q \<le> length q - 1"
+	unfolding degree_def by simp
+      from ath[OF lgpq lgq0 dql, unfolded pnormal_degree[OF lq, symmetric]] divides_degree[OF l] have "poly q = poly []" by auto
+      hence ?rhs unfolding poly_zero by (simp add: list_all_iff list_ex_iff)}
+    ultimately have ?rhs by blast }
+  ultimately show "?lhs \<equiv> ?rhs" by - (atomize (full), blast)
+qed
+
+lemma poly_divides_conv1:
+  assumes a0: "a\<noteq> (0::complex)" and pp': "(p::complex list) divides p'"
+  and qrp': "\<And>x. a * poly q x - poly p' x \<equiv> poly r x"
+  shows "p divides q \<equiv> p divides (r::complex list)" (is "?lhs \<equiv> ?rhs")
+proof-
+  {
+  from pp' obtain t where t: "poly p' = poly (p *** t)"
+    unfolding divides_def by blast
+  {assume l: ?lhs
+    then obtain u where u: "poly q = poly (p *** u)" unfolding divides_def by blast
+     have "poly r = poly (p *** ((a %* u) +++ (-- t)))"
+       using u qrp' t
+       by - (rule ext,
+     then have ?rhs unfolding divides_def by blast}
+  moreover
+  {assume r: ?rhs
+    then obtain u where u: "poly r = poly (p *** u)" unfolding divides_def by blast
+    from u t qrp' a0 have "poly q = poly (p *** ((1/a) %* (u +++ t)))"
+      by - (rule ext, atomize (full), simp add: poly_mult poly_add poly_cmult field_simps)
+    hence ?lhs  unfolding divides_def by blast}
+  ultimately have "?lhs = ?rhs" by blast }
+thus "?lhs \<equiv> ?rhs"  by - (atomize(full), blast)
+qed
+
+lemma basic_cqe_conv1:
+  "(\<exists>x. poly p x = 0 \<and> poly [] x \<noteq> 0) \<equiv> False"
+  "(\<exists>x. poly [] x \<noteq> 0) \<equiv> False"
+  "(\<exists>x. poly [c] x \<noteq> 0) \<equiv> c\<noteq>0"
+  "(\<exists>x. poly [] x = 0) \<equiv> True"
+  "(\<exists>x. poly [c] x = 0) \<equiv> c = 0" by simp_all
+
+lemma basic_cqe_conv2:
+  assumes l:"last (a#b#p) \<noteq> 0"
+  shows "(\<exists>x. poly (a#b#p) x = (0::complex)) \<equiv> True"
+proof-
+  {fix h t
+    assume h: "h\<noteq>0" "list_all (\<lambda>c. c=(0::complex)) t"  "a#b#p = h#t"
+    hence "list_all (\<lambda>c. c= 0) (b#p)" by simp
+    moreover have "last (b#p) \<in> set (b#p)" by simp
+    ultimately have "last (b#p) = 0" by (simp add: list_all_iff)
+    with l have False by simp}
+  hence th: "\<not> (\<exists> h t. h\<noteq>0 \<and> list_all (\<lambda>c. c=0) t \<and> a#b#p = h#t)"
+    by blast
+  from fundamental_theorem_of_algebra_alt[OF th]
+  show "(\<exists>x. poly (a#b#p) x = (0::complex)) \<equiv> True" by auto
+qed
+
+lemma  basic_cqe_conv_2b: "(\<exists>x. poly p x \<noteq> (0::complex)) \<equiv> (list_ex (\<lambda>c. c \<noteq> 0) p)"
+proof-
+  have "\<not> (list_ex (\<lambda>c. c \<noteq> 0) p) \<longleftrightarrow> poly p = poly []"
+    by (simp add: poly_zero list_all_iff list_ex_iff)
+  also have "\<dots> \<longleftrightarrow> (\<not> (\<exists>x. poly p x \<noteq> 0))" by (auto intro: ext)
+  finally show "(\<exists>x. poly p x \<noteq> (0::complex)) \<equiv> (list_ex (\<lambda>c. c \<noteq> 0) p)"
+    by - (atomize (full), blast)
+qed
+
+lemma basic_cqe_conv3:
+  fixes p q :: "complex list"
+  assumes l: "last (a#p) \<noteq> 0"
+  shows "(\<exists>x. poly (a#p) x =0 \<and> poly q x \<noteq> 0) \<equiv> \<not> ((a#p) divides (q %^ (length p)))"
+proof-
+  note np = pnormalize_eq[OF l]
+  {assume "poly (a#p) = poly []" hence False using l
+      unfolding poly_zero apply (auto simp add: list_all_iff del: last.simps)
+      apply (cases p, simp_all) done}
+  then have p0: "poly (a#p) \<noteq> poly []"  by blast
+  from np have dp:"degree (a#p) = length p" by (simp add: degree_def)
+  from nullstellensatz_univariate[of "a#p" q] p0 dp
+  show "(\<exists>x. poly (a#p) x =0 \<and> poly q x \<noteq> 0) \<equiv> \<not> ((a#p) divides (q %^ (length p)))"
+    by - (atomize (full), auto)
+qed
+
+lemma basic_cqe_conv4:
+  fixes p q :: "complex list"
+  assumes h: "\<And>x. poly (q %^ n) x \<equiv> poly r x"
+  shows "p divides (q %^ n) \<equiv> p divides r"
+proof-
+  from h have "poly (q %^ n) = poly r" by (auto intro: ext)
+  thus "p divides (q %^ n) \<equiv> p divides r" unfolding divides_def by simp
+qed
+
+lemma pmult_Cons_Cons: "((a::complex)#b#p) *** q = (a %*q) +++ (0#((b#p) *** q))"
+  by simp
+
+lemma elim_neg_conv: "- z \<equiv> (-1) * (z::complex)" by simp
+lemma eqT_intr: "PROP P \<Longrightarrow> (True \<Longrightarrow> PROP P )" "PROP P \<Longrightarrow> True" by blast+
+lemma negate_negate_rule: "Trueprop P \<equiv> \<not> P \<equiv> False" by (atomize (full), auto)
+lemma last_simps: "last [x] = x" "last (x#y#ys) = last (y#ys)" by simp_all
+lemma length_simps: "length [] = 0" "length (x#y#xs) = length xs + 2" "length [x] = 1" by simp_all
+
+lemma complex_entire: "(z::complex) \<noteq> 0 \<and> w \<noteq> 0 \<equiv> z*w \<noteq> 0" by simp
+lemma resolve_eq_ne: "(P \<equiv> True) \<equiv> (\<not>P \<equiv> False)" "(P \<equiv> False) \<equiv> (\<not>P \<equiv> True)"
+  by (atomize (full)) simp_all
+lemma cqe_conv1: "poly [] x = 0 \<longleftrightarrow> True"  by simp
+lemma cqe_conv2: "(p \<Longrightarrow> (q \<equiv> r)) \<equiv> ((p \<and> q) \<equiv> (p \<and> r))"  (is "?l \<equiv> ?r")
+proof
+  assume "p \<Longrightarrow> q \<equiv> r" thus "p \<and> q \<equiv> p \<and> r" apply - apply (atomize (full)) by blast
+next
+  assume "p \<and> q \<equiv> p \<and> r" "p"
+  thus "q \<equiv> r" apply - apply (atomize (full)) apply blast done
+qed
+lemma poly_const_conv: "poly [c] (x::complex) = y \<longleftrightarrow> c = y" by simp
+
+end
\ No newline at end of file```