src/HOL/Library/Formal_Power_Series.thy

farewell to class recpower

(*  Title:      Formal_Power_Series.thy
    Author:     Amine Chaieb, University of Cambridge
*)

header{* A formalization of formal power series *}

theory Formal_Power_Series
imports Main Fact Parity
begin

subsection {* The type of formal power series*}

typedef (open) 'a fps = "{f :: nat \<Rightarrow> 'a. True}"
  morphisms fps_nth Abs_fps
  by simp

notation fps_nth (infixl "$" 75)

lemma expand_fps_eq: "p = q \<longleftrightarrow> (\<forall>n. p $ n = q $ n)"
  by (simp add: fps_nth_inject [symmetric] expand_fun_eq)

lemma fps_ext: "(\<And>n. p $ n = q $ n) \<Longrightarrow> p = q"
  by (simp add: expand_fps_eq)

lemma fps_nth_Abs_fps [simp]: "Abs_fps f $ n = f n"
  by (simp add: Abs_fps_inverse)

text{* Definition of the basic elements 0 and 1 and the basic operations of addition, negation and multiplication *}

instantiation fps :: (zero)  zero
begin

definition fps_zero_def:
  "0 = Abs_fps (\<lambda>n. 0)"

instance ..
end

lemma fps_zero_nth [simp]: "0 $ n = 0"
  unfolding fps_zero_def by simp

instantiation fps :: ("{one,zero}")  one
begin

definition fps_one_def:
  "1 = Abs_fps (\<lambda>n. if n = 0 then 1 else 0)"

instance ..
end

lemma fps_one_nth [simp]: "1 $ n = (if n = 0 then 1 else 0)"
  unfolding fps_one_def by simp

instantiation fps :: (plus)  plus
begin

definition fps_plus_def:
  "op + = (\<lambda>f g. Abs_fps (\<lambda>n. f $ n + g $ n))"

instance ..
end

lemma fps_add_nth [simp]: "(f + g) $ n = f $ n + g $ n"
  unfolding fps_plus_def by simp

instantiation fps :: (minus) minus
begin

definition fps_minus_def:
  "op - = (\<lambda>f g. Abs_fps (\<lambda>n. f $ n - g $ n))"

instance ..
end

lemma fps_sub_nth [simp]: "(f - g) $ n = f $ n - g $ n"
  unfolding fps_minus_def by simp

instantiation fps :: (uminus) uminus
begin

definition fps_uminus_def:
  "uminus = (\<lambda>f. Abs_fps (\<lambda>n. - (f $ n)))"

instance ..
end

lemma fps_neg_nth [simp]: "(- f) $ n = - (f $ n)"
  unfolding fps_uminus_def by simp

instantiation fps :: ("{comm_monoid_add, times}")  times
begin

definition fps_times_def:
  "op * = (\<lambda>f g. Abs_fps (\<lambda>n. \<Sum>i=0..n. f $ i * g $ (n - i)))"

instance ..
end

lemma fps_mult_nth: "(f * g) $ n = (\<Sum>i=0..n. f$i * g$(n - i))"
  unfolding fps_times_def by simp

declare atLeastAtMost_iff[presburger]
declare Bex_def[presburger]
declare Ball_def[presburger]

lemma mult_delta_left:
  fixes x y :: "'a::mult_zero"
  shows "(if b then x else 0) * y = (if b then x * y else 0)"
  by simp

lemma mult_delta_right:
  fixes x y :: "'a::mult_zero"
  shows "x * (if b then y else 0) = (if b then x * y else 0)"
  by simp

lemma cond_value_iff: "f (if b then x else y) = (if b then f x else f y)"
  by auto
lemma cond_application_beta: "(if b then f else g) x = (if b then f x else g x)"
  by auto

subsection{* Formal power series form a commutative ring with unity, if the range of sequences
  they represent is a commutative ring with unity*}

instance fps :: (semigroup_add) semigroup_add
proof
  fix a b c :: "'a fps" show "a + b + c = a + (b + c)"
    by (simp add: fps_ext add_assoc)
qed

instance fps :: (ab_semigroup_add) ab_semigroup_add
proof
  fix a b :: "'a fps" show "a + b = b + a"
    by (simp add: fps_ext add_commute)
qed

lemma fps_mult_assoc_lemma:
  fixes k :: nat and f :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> 'a::comm_monoid_add"
  shows "(\<Sum>j=0..k. \<Sum>i=0..j. f i (j - i) (n - j)) =
         (\<Sum>j=0..k. \<Sum>i=0..k - j. f j i (n - j - i))"
proof (induct k)
  case 0 show ?case by simp
next
  case (Suc k) thus ?case
    by (simp add: Suc_diff_le setsum_addf add_assoc
             cong: strong_setsum_cong)
qed

instance fps :: (semiring_0) semigroup_mult
proof
  fix a b c :: "'a fps"
  show "(a * b) * c = a * (b * c)"
  proof (rule fps_ext)
    fix n :: nat
    have "(\<Sum>j=0..n. \<Sum>i=0..j. a$i * b$(j - i) * c$(n - j)) =
          (\<Sum>j=0..n. \<Sum>i=0..n - j. a$j * b$i * c$(n - j - i))"
      by (rule fps_mult_assoc_lemma)
    thus "((a * b) * c) $ n = (a * (b * c)) $ n"
      by (simp add: fps_mult_nth setsum_right_distrib
                    setsum_left_distrib mult_assoc)
  qed
qed

lemma fps_mult_commute_lemma:
  fixes n :: nat and f :: "nat \<Rightarrow> nat \<Rightarrow> 'a::comm_monoid_add"
  shows "(\<Sum>i=0..n. f i (n - i)) = (\<Sum>i=0..n. f (n - i) i)"
proof (rule setsum_reindex_cong)
  show "inj_on (\<lambda>i. n - i) {0..n}"
    by (rule inj_onI) simp
  show "{0..n} = (\<lambda>i. n - i) ` {0..n}"
    by (auto, rule_tac x="n - x" in image_eqI, simp_all)
next
  fix i assume "i \<in> {0..n}"
  hence "n - (n - i) = i" by simp
  thus "f (n - i) i = f (n - i) (n - (n - i))" by simp
qed

instance fps :: (comm_semiring_0) ab_semigroup_mult
proof
  fix a b :: "'a fps"
  show "a * b = b * a"
  proof (rule fps_ext)
    fix n :: nat
    have "(\<Sum>i=0..n. a$i * b$(n - i)) = (\<Sum>i=0..n. a$(n - i) * b$i)"
      by (rule fps_mult_commute_lemma)
    thus "(a * b) $ n = (b * a) $ n"
      by (simp add: fps_mult_nth mult_commute)
  qed
qed

instance fps :: (monoid_add) monoid_add
proof
  fix a :: "'a fps" show "0 + a = a "
    by (simp add: fps_ext)
next
  fix a :: "'a fps" show "a + 0 = a "
    by (simp add: fps_ext)
qed

instance fps :: (comm_monoid_add) comm_monoid_add
proof
  fix a :: "'a fps" show "0 + a = a "
    by (simp add: fps_ext)
qed

instance fps :: (semiring_1) monoid_mult
proof
  fix a :: "'a fps" show "1 * a = a"
    by (simp add: fps_ext fps_mult_nth mult_delta_left setsum_delta)
next
  fix a :: "'a fps" show "a * 1 = a"
    by (simp add: fps_ext fps_mult_nth mult_delta_right setsum_delta')
qed

instance fps :: (cancel_semigroup_add) cancel_semigroup_add
proof
  fix a b c :: "'a fps"
  assume "a + b = a + c" then show "b = c"
    by (simp add: expand_fps_eq)
next
  fix a b c :: "'a fps"
  assume "b + a = c + a" then show "b = c"
    by (simp add: expand_fps_eq)
qed

instance fps :: (cancel_ab_semigroup_add) cancel_ab_semigroup_add
proof
  fix a b c :: "'a fps"
  assume "a + b = a + c" then show "b = c"
    by (simp add: expand_fps_eq)
qed

instance fps :: (cancel_comm_monoid_add) cancel_comm_monoid_add ..

instance fps :: (group_add) group_add
proof
  fix a :: "'a fps" show "- a + a = 0"
    by (simp add: fps_ext)
next
  fix a b :: "'a fps" show "a - b = a + - b"
    by (simp add: fps_ext diff_minus)
qed

instance fps :: (ab_group_add) ab_group_add
proof
  fix a :: "'a fps"
  show "- a + a = 0"
    by (simp add: fps_ext)
next
  fix a b :: "'a fps"
  show "a - b = a + - b"
    by (simp add: fps_ext)
qed

instance fps :: (zero_neq_one) zero_neq_one
  by default (simp add: expand_fps_eq)

instance fps :: (semiring_0) semiring
proof
  fix a b c :: "'a fps"
  show "(a + b) * c = a * c + b * c"
    by (simp add: expand_fps_eq fps_mult_nth left_distrib setsum_addf)
next
  fix a b c :: "'a fps"
  show "a * (b + c) = a * b + a * c"
    by (simp add: expand_fps_eq fps_mult_nth right_distrib setsum_addf)
qed

instance fps :: (semiring_0) semiring_0
proof
  fix a:: "'a fps" show "0 * a = 0"
    by (simp add: fps_ext fps_mult_nth)
next
  fix a:: "'a fps" show "a * 0 = 0"
    by (simp add: fps_ext fps_mult_nth)
qed

instance fps :: (semiring_0_cancel) semiring_0_cancel ..

subsection {* Selection of the nth power of the implicit variable in the infinite sum*}

lemma fps_nonzero_nth: "f \<noteq> 0 \<longleftrightarrow> (\<exists> n. f $n \<noteq> 0)"
  by (simp add: expand_fps_eq)

lemma fps_nonzero_nth_minimal:
  "f \<noteq> 0 \<longleftrightarrow> (\<exists>n. f $ n \<noteq> 0 \<and> (\<forall>m<n. f $ m = 0))"
proof
  let ?n = "LEAST n. f $ n \<noteq> 0"
  assume "f \<noteq> 0"
  then have "\<exists>n. f $ n \<noteq> 0"
    by (simp add: fps_nonzero_nth)
  then have "f $ ?n \<noteq> 0"
    by (rule LeastI_ex)
  moreover have "\<forall>m<?n. f $ m = 0"
    by (auto dest: not_less_Least)
  ultimately have "f $ ?n \<noteq> 0 \<and> (\<forall>m<?n. f $ m = 0)" ..
  then show "\<exists>n. f $ n \<noteq> 0 \<and> (\<forall>m<n. f $ m = 0)" ..
next
  assume "\<exists>n. f $ n \<noteq> 0 \<and> (\<forall>m<n. f $ m = 0)"
  then show "f \<noteq> 0" by (auto simp add: expand_fps_eq)
qed

lemma fps_eq_iff: "f = g \<longleftrightarrow> (\<forall>n. f $ n = g $n)"
  by (rule expand_fps_eq)

lemma fps_setsum_nth: "(setsum f S) $ n = setsum (\<lambda>k. (f k) $ n) S"
proof (cases "finite S")
  assume "\<not> finite S" then show ?thesis by simp
next
  assume "finite S"
  then show ?thesis by (induct set: finite) auto
qed

subsection{* Injection of the basic ring elements and multiplication by scalars *}

definition
  "fps_const c = Abs_fps (\<lambda>n. if n = 0 then c else 0)"

lemma fps_nth_fps_const [simp]: "fps_const c $ n = (if n = 0 then c else 0)"
  unfolding fps_const_def by simp

lemma fps_const_0_eq_0 [simp]: "fps_const 0 = 0"
  by (simp add: fps_ext)

lemma fps_const_1_eq_1 [simp]: "fps_const 1 = 1"
  by (simp add: fps_ext)

lemma fps_const_neg [simp]: "- (fps_const (c::'a::ring)) = fps_const (- c)"
  by (simp add: fps_ext)

lemma fps_const_add [simp]: "fps_const (c::'a\<Colon>monoid_add) + fps_const d = fps_const (c + d)"
  by (simp add: fps_ext)

lemma fps_const_mult[simp]: "fps_const (c::'a\<Colon>ring) * fps_const d = fps_const (c * d)"
  by (simp add: fps_eq_iff fps_mult_nth setsum_0')

lemma fps_const_add_left: "fps_const (c::'a\<Colon>monoid_add) + f = Abs_fps (\<lambda>n. if n = 0 then c + f$0 else f$n)"
  by (simp add: fps_ext)

lemma fps_const_add_right: "f + fps_const (c::'a\<Colon>monoid_add) = Abs_fps (\<lambda>n. if n = 0 then f$0 + c else f$n)"
  by (simp add: fps_ext)

lemma fps_const_mult_left: "fps_const (c::'a\<Colon>semiring_0) * f = Abs_fps (\<lambda>n. c * f$n)"
  unfolding fps_eq_iff fps_mult_nth
  by (simp add: fps_const_def mult_delta_left setsum_delta)

lemma fps_const_mult_right: "f * fps_const (c::'a\<Colon>semiring_0) = Abs_fps (\<lambda>n. f$n * c)"
  unfolding fps_eq_iff fps_mult_nth
  by (simp add: fps_const_def mult_delta_right setsum_delta')

lemma fps_mult_left_const_nth [simp]: "(fps_const (c::'a::semiring_1) * f)$n = c* f$n"
  by (simp add: fps_mult_nth mult_delta_left setsum_delta)

lemma fps_mult_right_const_nth [simp]: "(f * fps_const (c::'a::semiring_1))$n = f$n * c"
  by (simp add: fps_mult_nth mult_delta_right setsum_delta')

subsection {* Formal power series form an integral domain*}

instance fps :: (ring) ring ..

instance fps :: (ring_1) ring_1
  by (intro_classes, auto simp add: diff_minus left_distrib)

instance fps :: (comm_ring_1) comm_ring_1
  by (intro_classes, auto simp add: diff_minus left_distrib)

instance fps :: (ring_no_zero_divisors) ring_no_zero_divisors
proof
  fix a b :: "'a fps"
  assume a0: "a \<noteq> 0" and b0: "b \<noteq> 0"
  then obtain i j where i: "a$i\<noteq>0" "\<forall>k<i. a$k=0"
    and j: "b$j \<noteq>0" "\<forall>k<j. b$k =0" unfolding fps_nonzero_nth_minimal
    by blast+
  have "(a * b) $ (i+j) = (\<Sum>k=0..i+j. a$k * b$(i+j-k))"
    by (rule fps_mult_nth)
  also have "\<dots> = (a$i * b$(i+j-i)) + (\<Sum>k\<in>{0..i+j}-{i}. a$k * b$(i+j-k))"
    by (rule setsum_diff1') simp_all
  also have "(\<Sum>k\<in>{0..i+j}-{i}. a$k * b$(i+j-k)) = 0"
    proof (rule setsum_0' [rule_format])
      fix k assume "k \<in> {0..i+j} - {i}"
      then have "k < i \<or> i+j-k < j" by auto
      then show "a$k * b$(i+j-k) = 0" using i j by auto
    qed
  also have "a$i * b$(i+j-i) + 0 = a$i * b$j" by simp
  also have "a$i * b$j \<noteq> 0" using i j by simp
  finally have "(a*b) $ (i+j) \<noteq> 0" .
  then show "a*b \<noteq> 0" unfolding fps_nonzero_nth by blast
qed

instance fps :: (idom) idom ..

instantiation fps :: (comm_ring_1) number_ring
begin
definition number_of_fps_def: "(number_of k::'a fps) = of_int k"

instance 
by (intro_classes, rule number_of_fps_def)
end

subsection{* Inverses of formal power series *}

declare setsum_cong[fundef_cong]


instantiation fps :: ("{comm_monoid_add,inverse, times, uminus}") inverse
begin

fun natfun_inverse:: "'a fps \<Rightarrow> nat \<Rightarrow> 'a" where
  "natfun_inverse f 0 = inverse (f$0)"
| "natfun_inverse f n = - inverse (f$0) * setsum (\<lambda>i. f$i * natfun_inverse f (n - i)) {1..n}"

definition fps_inverse_def:
  "inverse f = (if f$0 = 0 then 0 else Abs_fps (natfun_inverse f))"
definition fps_divide_def: "divide = (\<lambda>(f::'a fps) g. f * inverse g)"
instance ..
end

lemma fps_inverse_zero[simp]:
  "inverse (0 :: 'a::{comm_monoid_add,inverse, times, uminus} fps) = 0"
  by (simp add: fps_ext fps_inverse_def)

lemma fps_inverse_one[simp]: "inverse (1 :: 'a::{division_ring,zero_neq_one} fps) = 1"
  apply (auto simp add: expand_fps_eq fps_inverse_def)
  by (case_tac n, auto)

instance fps :: ("{comm_monoid_add,inverse, times, uminus}")  division_by_zero
  by default (rule fps_inverse_zero)

lemma inverse_mult_eq_1[intro]: assumes f0: "f$0 \<noteq> (0::'a::field)"
  shows "inverse f * f = 1"
proof-
  have c: "inverse f * f = f * inverse f" by (simp add: mult_commute)
  from f0 have ifn: "\<And>n. inverse f $ n = natfun_inverse f n"
    by (simp add: fps_inverse_def)
  from f0 have th0: "(inverse f * f) $ 0 = 1"
    by (simp add: fps_mult_nth fps_inverse_def)
  {fix n::nat assume np: "n >0 "
    from np have eq: "{0..n} = {0} \<union> {1 .. n}" by auto
    have d: "{0} \<inter> {1 .. n} = {}" by auto
    have f: "finite {0::nat}" "finite {1..n}" by auto
    from f0 np have th0: "- (inverse f$n) =
      (setsum (\<lambda>i. f$i * natfun_inverse f (n - i)) {1..n}) / (f$0)"
      by (cases n, simp, simp add: divide_inverse fps_inverse_def)
    from th0[symmetric, unfolded nonzero_divide_eq_eq[OF f0]]
    have th1: "setsum (\<lambda>i. f$i * natfun_inverse f (n - i)) {1..n} =
      - (f$0) * (inverse f)$n"
      by (simp add: ring_simps)
    have "(f * inverse f) $ n = (\<Sum>i = 0..n. f $i * natfun_inverse f (n - i))"
      unfolding fps_mult_nth ifn ..
    also have "\<dots> = f$0 * natfun_inverse f n
      + (\<Sum>i = 1..n. f$i * natfun_inverse f (n-i))"
      unfolding setsum_Un_disjoint[OF f d, unfolded eq[symmetric]]
      by simp
    also have "\<dots> = 0" unfolding th1 ifn by simp
    finally have "(inverse f * f)$n = 0" unfolding c . }
  with th0 show ?thesis by (simp add: fps_eq_iff)
qed

lemma fps_inverse_0_iff[simp]: "(inverse f)$0 = (0::'a::division_ring) \<longleftrightarrow> f$0 = 0"
  by (simp add: fps_inverse_def nonzero_imp_inverse_nonzero)

lemma fps_inverse_eq_0_iff[simp]: "inverse f = (0:: ('a::field) fps) \<longleftrightarrow> f $0 = 0"
proof-
  {assume "f$0 = 0" hence "inverse f = 0" by (simp add: fps_inverse_def)}
  moreover
  {assume h: "inverse f = 0" and c: "f $0 \<noteq> 0"
    from inverse_mult_eq_1[OF c] h have False by simp}
  ultimately show ?thesis by blast
qed

lemma fps_inverse_idempotent[intro]: assumes f0: "f$0 \<noteq> (0::'a::field)"
  shows "inverse (inverse f) = f"
proof-
  from f0 have if0: "inverse f $ 0 \<noteq> 0" by simp
  from inverse_mult_eq_1[OF f0] inverse_mult_eq_1[OF if0]
  have th0: "inverse f * f = inverse f * inverse (inverse f)"   by (simp add: mult_ac)
  then show ?thesis using f0 unfolding mult_cancel_left by simp
qed

lemma fps_inverse_unique: assumes f0: "f$0 \<noteq> (0::'a::field)" and fg: "f*g = 1"
  shows "inverse f = g"
proof-
  from inverse_mult_eq_1[OF f0] fg
  have th0: "inverse f * f = g * f" by (simp add: mult_ac)
  then show ?thesis using f0  unfolding mult_cancel_right
    by (auto simp add: expand_fps_eq)
qed

lemma fps_inverse_gp: "inverse (Abs_fps(\<lambda>n. (1::'a::field)))
  = Abs_fps (\<lambda>n. if n= 0 then 1 else if n=1 then - 1 else 0)"
  apply (rule fps_inverse_unique)
  apply simp
  apply (simp add: fps_eq_iff fps_mult_nth)
proof(clarsimp)
  fix n::nat assume n: "n > 0"
  let ?f = "\<lambda>i. if n = i then (1\<Colon>'a) else if n - i = 1 then - 1 else 0"
  let ?g = "\<lambda>i. if i = n then 1 else if i=n - 1 then - 1 else 0"
  let ?h = "\<lambda>i. if i=n - 1 then - 1 else 0"
  have th1: "setsum ?f {0..n} = setsum ?g {0..n}"
    by (rule setsum_cong2) auto
  have th2: "setsum ?g {0..n - 1} = setsum ?h {0..n - 1}"
    using n apply - by (rule setsum_cong2) auto
  have eq: "{0 .. n} = {0.. n - 1} \<union> {n}" by auto
  from n have d: "{0.. n - 1} \<inter> {n} = {}" by auto
  have f: "finite {0.. n - 1}" "finite {n}" by auto
  show "setsum ?f {0..n} = 0"
    unfolding th1
    apply (simp add: setsum_Un_disjoint[OF f d, unfolded eq[symmetric]] del: One_nat_def)
    unfolding th2
    by(simp add: setsum_delta)
qed

subsection{* Formal Derivatives, and the MacLaurin theorem around 0*}

definition "fps_deriv f = Abs_fps (\<lambda>n. of_nat (n + 1) * f $ (n + 1))"

lemma fps_deriv_nth[simp]: "fps_deriv f $ n = of_nat (n +1) * f $ (n+1)" by (simp add: fps_deriv_def)

lemma fps_deriv_linear[simp]: "fps_deriv (fps_const (a::'a::comm_semiring_1) * f + fps_const b * g) = fps_const a * fps_deriv f + fps_const b * fps_deriv g"
  unfolding fps_eq_iff fps_add_nth  fps_const_mult_left fps_deriv_nth by (simp add: ring_simps)

lemma fps_deriv_mult[simp]:
  fixes f :: "('a :: comm_ring_1) fps"
  shows "fps_deriv (f * g) = f * fps_deriv g + fps_deriv f * g"
proof-
  let ?D = "fps_deriv"
  {fix n::nat
    let ?Zn = "{0 ..n}"
    let ?Zn1 = "{0 .. n + 1}"
    let ?f = "\<lambda>i. i + 1"
    have fi: "inj_on ?f {0..n}" by (simp add: inj_on_def)
    have eq: "{1.. n+1} = ?f ` {0..n}" by auto
    let ?g = "\<lambda>i. of_nat (i+1) * g $ (i+1) * f $ (n - i) +
        of_nat (i+1)* f $ (i+1) * g $ (n - i)"
    let ?h = "\<lambda>i. of_nat i * g $ i * f $ ((n+1) - i) +
        of_nat i* f $ i * g $ ((n + 1) - i)"
    {fix k assume k: "k \<in> {0..n}"
      have "?h (k + 1) = ?g k" using k by auto}
    note th0 = this
    have eq': "{0..n +1}- {1 .. n+1} = {0}" by auto
    have s0: "setsum (\<lambda>i. of_nat i * f $ i * g $ (n + 1 - i)) ?Zn1 = setsum (\<lambda>i. of_nat (n + 1 - i) * f $ (n + 1 - i) * g $ i) ?Zn1"
      apply (rule setsum_reindex_cong[where f="\<lambda>i. n + 1 - i"])
      apply (simp add: inj_on_def Ball_def)
      apply presburger
      apply (rule set_ext)
      apply (presburger add: image_iff)
      by simp
    have s1: "setsum (\<lambda>i. f $ i * g $ (n + 1 - i)) ?Zn1 = setsum (\<lambda>i. f $ (n + 1 - i) * g $ i) ?Zn1"
      apply (rule setsum_reindex_cong[where f="\<lambda>i. n + 1 - i"])
      apply (simp add: inj_on_def Ball_def)
      apply presburger
      apply (rule set_ext)
      apply (presburger add: image_iff)
      by simp
    have "(f * ?D g + ?D f * g)$n = (?D g * f + ?D f * g)$n" by (simp only: mult_commute)
    also have "\<dots> = (\<Sum>i = 0..n. ?g i)"
      by (simp add: fps_mult_nth setsum_addf[symmetric])
    also have "\<dots> = setsum ?h {1..n+1}"
      using th0 setsum_reindex_cong[OF fi eq, of "?g" "?h"] by auto
    also have "\<dots> = setsum ?h {0..n+1}"
      apply (rule setsum_mono_zero_left)
      apply simp
      apply (simp add: subset_eq)
      unfolding eq'
      by simp
    also have "\<dots> = (fps_deriv (f * g)) $ n"
      apply (simp only: fps_deriv_nth fps_mult_nth setsum_addf)
      unfolding s0 s1
      unfolding setsum_addf[symmetric] setsum_right_distrib
      apply (rule setsum_cong2)
      by (auto simp add: of_nat_diff ring_simps)
    finally have "(f * ?D g + ?D f * g) $ n = ?D (f*g) $ n" .}
  then show ?thesis unfolding fps_eq_iff by auto
qed

lemma fps_deriv_neg[simp]: "fps_deriv (- (f:: ('a:: comm_ring_1) fps)) = - (fps_deriv f)"
  by (simp add: fps_eq_iff fps_deriv_def)
lemma fps_deriv_add[simp]: "fps_deriv ((f:: ('a::comm_ring_1) fps) + g) = fps_deriv f + fps_deriv g"
  using fps_deriv_linear[of 1 f 1 g] by simp

lemma fps_deriv_sub[simp]: "fps_deriv ((f:: ('a::comm_ring_1) fps) - g) = fps_deriv f - fps_deriv g"
  unfolding diff_minus by simp

lemma fps_deriv_const[simp]: "fps_deriv (fps_const c) = 0"
  by (simp add: fps_ext fps_deriv_def fps_const_def)

lemma fps_deriv_mult_const_left[simp]: "fps_deriv (fps_const (c::'a::comm_ring_1) * f) = fps_const c * fps_deriv f"
  by simp

lemma fps_deriv_0[simp]: "fps_deriv 0 = 0"
  by (simp add: fps_deriv_def fps_eq_iff)

lemma fps_deriv_1[simp]: "fps_deriv 1 = 0"
  by (simp add: fps_deriv_def fps_eq_iff )

lemma fps_deriv_mult_const_right[simp]: "fps_deriv (f * fps_const (c::'a::comm_ring_1)) = fps_deriv f * fps_const c"
  by simp

lemma fps_deriv_setsum: "fps_deriv (setsum f S) = setsum (\<lambda>i. fps_deriv (f i :: ('a::comm_ring_1) fps)) S"
proof-
  {assume "\<not> finite S" hence ?thesis by simp}
  moreover
  {assume fS: "finite S"
    have ?thesis  by (induct rule: finite_induct[OF fS], simp_all)}
  ultimately show ?thesis by blast
qed

lemma fps_deriv_eq_0_iff[simp]: "fps_deriv f = 0 \<longleftrightarrow> (f = fps_const (f$0 :: 'a::{idom,semiring_char_0}))"
proof-
  {assume "f= fps_const (f$0)" hence "fps_deriv f = fps_deriv (fps_const (f$0))" by simp
    hence "fps_deriv f = 0" by simp }
  moreover
  {assume z: "fps_deriv f = 0"
    hence "\<forall>n. (fps_deriv f)$n = 0" by simp
    hence "\<forall>n. f$(n+1) = 0" by (simp del: of_nat_Suc of_nat_add One_nat_def)
    hence "f = fps_const (f$0)"
      apply (clarsimp simp add: fps_eq_iff fps_const_def)
      apply (erule_tac x="n - 1" in allE)
      by simp}
  ultimately show ?thesis by blast
qed

lemma fps_deriv_eq_iff:
  fixes f:: "('a::{idom,semiring_char_0}) fps"
  shows "fps_deriv f = fps_deriv g \<longleftrightarrow> (f = fps_const(f$0 - g$0) + g)"
proof-
  have "fps_deriv f = fps_deriv g \<longleftrightarrow> fps_deriv (f - g) = 0" by simp
  also have "\<dots> \<longleftrightarrow> f - g = fps_const ((f-g)$0)" unfolding fps_deriv_eq_0_iff ..
  finally show ?thesis by (simp add: ring_simps)
qed

lemma fps_deriv_eq_iff_ex: "(fps_deriv f = fps_deriv g) \<longleftrightarrow> (\<exists>(c::'a::{idom,semiring_char_0}). f = fps_const c + g)"
  apply auto unfolding fps_deriv_eq_iff by blast


fun fps_nth_deriv :: "nat \<Rightarrow> ('a::semiring_1) fps \<Rightarrow> 'a fps" where
  "fps_nth_deriv 0 f = f"
| "fps_nth_deriv (Suc n) f = fps_nth_deriv n (fps_deriv f)"

lemma fps_nth_deriv_commute: "fps_nth_deriv (Suc n) f = fps_deriv (fps_nth_deriv n f)"
  by (induct n arbitrary: f, auto)

lemma fps_nth_deriv_linear[simp]: "fps_nth_deriv n (fps_const (a::'a::comm_semiring_1) * f + fps_const b * g) = fps_const a * fps_nth_deriv n f + fps_const b * fps_nth_deriv n g"
  by (induct n arbitrary: f g, auto simp add: fps_nth_deriv_commute)

lemma fps_nth_deriv_neg[simp]: "fps_nth_deriv n (- (f:: ('a:: comm_ring_1) fps)) = - (fps_nth_deriv n f)"
  by (induct n arbitrary: f, simp_all)

lemma fps_nth_deriv_add[simp]: "fps_nth_deriv n ((f:: ('a::comm_ring_1) fps) + g) = fps_nth_deriv n f + fps_nth_deriv n g"
  using fps_nth_deriv_linear[of n 1 f 1 g] by simp

lemma fps_nth_deriv_sub[simp]: "fps_nth_deriv n ((f:: ('a::comm_ring_1) fps) - g) = fps_nth_deriv n f - fps_nth_deriv n g"
  unfolding diff_minus fps_nth_deriv_add by simp

lemma fps_nth_deriv_0[simp]: "fps_nth_deriv n 0 = 0"
  by (induct n, simp_all )

lemma fps_nth_deriv_1[simp]: "fps_nth_deriv n 1 = (if n = 0 then 1 else 0)"
  by (induct n, simp_all )

lemma fps_nth_deriv_const[simp]: "fps_nth_deriv n (fps_const c) = (if n = 0 then fps_const c else 0)"
  by (cases n, simp_all)

lemma fps_nth_deriv_mult_const_left[simp]: "fps_nth_deriv n (fps_const (c::'a::comm_ring_1) * f) = fps_const c * fps_nth_deriv n f"
  using fps_nth_deriv_linear[of n "c" f 0 0 ] by simp

lemma fps_nth_deriv_mult_const_right[simp]: "fps_nth_deriv n (f * fps_const (c::'a::comm_ring_1)) = fps_nth_deriv n f * fps_const c"
  using fps_nth_deriv_linear[of n "c" f 0 0] by (simp add: mult_commute)

lemma fps_nth_deriv_setsum: "fps_nth_deriv n (setsum f S) = setsum (\<lambda>i. fps_nth_deriv n (f i :: ('a::comm_ring_1) fps)) S"
proof-
  {assume "\<not> finite S" hence ?thesis by simp}
  moreover
  {assume fS: "finite S"
    have ?thesis  by (induct rule: finite_induct[OF fS], simp_all)}
  ultimately show ?thesis by blast
qed

lemma fps_deriv_maclauren_0: "(fps_nth_deriv k (f:: ('a::comm_semiring_1) fps)) $ 0 = of_nat (fact k) * f$(k)"
  by (induct k arbitrary: f) (auto simp add: ring_simps of_nat_mult)

subsection {* Powers*}

lemma fps_power_zeroth_eq_one: "a$0 =1 \<Longrightarrow> a^n $ 0 = (1::'a::semiring_1)"
  by (induct n, auto simp add: expand_fps_eq fps_mult_nth)

lemma fps_power_first_eq: "(a:: 'a::comm_ring_1 fps)$0 =1 \<Longrightarrow> a^n $ 1 = of_nat n * a$1"
proof(induct n)
  case 0 thus ?case by simp
next
  case (Suc n)
  note h = Suc.hyps[OF `a$0 = 1`]
  show ?case unfolding power_Suc fps_mult_nth
    using h `a$0 = 1`  fps_power_zeroth_eq_one[OF `a$0=1`] by (simp add: ring_simps)
qed

lemma startsby_one_power:"a $ 0 = (1::'a::comm_ring_1) \<Longrightarrow> a^n $ 0 = 1"
  by (induct n, auto simp add: fps_mult_nth)

lemma startsby_zero_power:"a $0 = (0::'a::comm_ring_1) \<Longrightarrow> n > 0 \<Longrightarrow> a^n $0 = 0"
  by (induct n, auto simp add: fps_mult_nth)

lemma startsby_power:"a $0 = (v::'a::{comm_ring_1}) \<Longrightarrow> a^n $0 = v^n"
  by (induct n, auto simp add: fps_mult_nth power_Suc)

lemma startsby_zero_power_iff[simp]:
  "a^n $0 = (0::'a::{idom}) \<longleftrightarrow> (n \<noteq> 0 \<and> a$0 = 0)"
apply (rule iffI)
apply (induct n, auto simp add: power_Suc fps_mult_nth)
by (rule startsby_zero_power, simp_all)

lemma startsby_zero_power_prefix:
  assumes a0: "a $0 = (0::'a::idom)"
  shows "\<forall>n < k. a ^ k $ n = 0"
  using a0
proof(induct k rule: nat_less_induct)
  fix k assume H: "\<forall>m<k. a $0 =  0 \<longrightarrow> (\<forall>n<m. a ^ m $ n = 0)" and a0: "a $0 = (0\<Colon>'a)"
  let ?ths = "\<forall>m<k. a ^ k $ m = 0"
  {assume "k = 0" then have ?ths by simp}
  moreover
  {fix l assume k: "k = Suc l"
    {fix m assume mk: "m < k"
      {assume "m=0" hence "a^k $ m = 0" using startsby_zero_power[of a k] k a0
	  by simp}
      moreover
      {assume m0: "m \<noteq> 0"
	have "a ^k $ m = (a^l * a) $m" by (simp add: k power_Suc mult_commute)
	also have "\<dots> = (\<Sum>i = 0..m. a ^ l $ i * a $ (m - i))" by (simp add: fps_mult_nth)
	also have "\<dots> = 0" apply (rule setsum_0')
	  apply auto
	  apply (case_tac "aa = m")
	  using a0
	  apply simp
	  apply (rule H[rule_format])
	  using a0 k mk by auto
	finally have "a^k $ m = 0" .}
    ultimately have "a^k $ m = 0" by blast}
    hence ?ths by blast}
  ultimately show ?ths by (cases k, auto)
qed

lemma startsby_zero_setsum_depends:
  assumes a0: "a $0 = (0::'a::idom)" and kn: "n \<ge> k"
  shows "setsum (\<lambda>i. (a ^ i)$k) {0 .. n} = setsum (\<lambda>i. (a ^ i)$k) {0 .. k}"
  apply (rule setsum_mono_zero_right)
  using kn apply auto
  apply (rule startsby_zero_power_prefix[rule_format, OF a0])
  by arith

lemma startsby_zero_power_nth_same: assumes a0: "a$0 = (0::'a::{idom})"
  shows "a^n $ n = (a$1) ^ n"
proof(induct n)
  case 0 thus ?case by (simp add: power_0)
next
  case (Suc n)
  have "a ^ Suc n $ (Suc n) = (a^n * a)$(Suc n)" by (simp add: ring_simps power_Suc)
  also have "\<dots> = setsum (\<lambda>i. a^n$i * a $ (Suc n - i)) {0.. Suc n}" by (simp add: fps_mult_nth)
  also have "\<dots> = setsum (\<lambda>i. a^n$i * a $ (Suc n - i)) {n .. Suc n}"
    apply (rule setsum_mono_zero_right)
    apply simp
    apply clarsimp
    apply clarsimp
    apply (rule startsby_zero_power_prefix[rule_format, OF a0])
    apply arith
    done
  also have "\<dots> = a^n $ n * a$1" using a0 by simp
  finally show ?case using Suc.hyps by (simp add: power_Suc)
qed

lemma fps_inverse_power:
  fixes a :: "('a::{field}) fps"
  shows "inverse (a^n) = inverse a ^ n"
proof-
  {assume a0: "a$0 = 0"
    hence eq: "inverse a = 0" by (simp add: fps_inverse_def)
    {assume "n = 0" hence ?thesis by simp}
    moreover
    {assume n: "n > 0"
      from startsby_zero_power[OF a0 n] eq a0 n have ?thesis
	by (simp add: fps_inverse_def)}
    ultimately have ?thesis by blast}
  moreover
  {assume a0: "a$0 \<noteq> 0"
    have ?thesis
      apply (rule fps_inverse_unique)
      apply (simp add: a0)
      unfolding power_mult_distrib[symmetric]
      apply (rule ssubst[where t = "a * inverse a" and s= 1])
      apply simp_all
      apply (subst mult_commute)
      by (rule inverse_mult_eq_1[OF a0])}
  ultimately show ?thesis by blast
qed

lemma fps_deriv_power: "fps_deriv (a ^ n) = fps_const (of_nat n :: 'a:: comm_ring_1) * fps_deriv a * a ^ (n - 1)"
  apply (induct n, auto simp add: power_Suc ring_simps fps_const_add[symmetric] simp del: fps_const_add)
  by (case_tac n, auto simp add: power_Suc ring_simps)

lemma fps_inverse_deriv:
  fixes a:: "('a :: field) fps"
  assumes a0: "a$0 \<noteq> 0"
  shows "fps_deriv (inverse a) = - fps_deriv a * inverse a ^ 2"
proof-
  from inverse_mult_eq_1[OF a0]
  have "fps_deriv (inverse a * a) = 0" by simp
  hence "inverse a * fps_deriv a + fps_deriv (inverse a) * a = 0" by simp
  hence "inverse a * (inverse a * fps_deriv a + fps_deriv (inverse a) * a) = 0"  by simp
  with inverse_mult_eq_1[OF a0]
  have "inverse a ^ 2 * fps_deriv a + fps_deriv (inverse a) = 0"
    unfolding power2_eq_square
    apply (simp add: ring_simps)
    by (simp add: mult_assoc[symmetric])
  hence "inverse a ^ 2 * fps_deriv a + fps_deriv (inverse a) - fps_deriv a * inverse a ^ 2 = 0 - fps_deriv a * inverse a ^ 2"
    by simp
  then show "fps_deriv (inverse a) = - fps_deriv a * inverse a ^ 2" by (simp add: ring_simps)
qed

lemma fps_inverse_mult:
  fixes a::"('a :: field) fps"
  shows "inverse (a * b) = inverse a * inverse b"
proof-
  {assume a0: "a$0 = 0" hence ab0: "(a*b)$0 = 0" by (simp add: fps_mult_nth)
    from a0 ab0 have th: "inverse a = 0" "inverse (a*b) = 0" by simp_all
    have ?thesis unfolding th by simp}
  moreover
  {assume b0: "b$0 = 0" hence ab0: "(a*b)$0 = 0" by (simp add: fps_mult_nth)
    from b0 ab0 have th: "inverse b = 0" "inverse (a*b) = 0" by simp_all
    have ?thesis unfolding th by simp}
  moreover
  {assume a0: "a$0 \<noteq> 0" and b0: "b$0 \<noteq> 0"
    from a0 b0 have ab0:"(a*b) $ 0 \<noteq> 0" by (simp  add: fps_mult_nth)
    from inverse_mult_eq_1[OF ab0]
    have "inverse (a*b) * (a*b) * inverse a * inverse b = 1 * inverse a * inverse b" by simp
    then have "inverse (a*b) * (inverse a * a) * (inverse b * b) = inverse a * inverse b"
      by (simp add: ring_simps)
    then have ?thesis using inverse_mult_eq_1[OF a0] inverse_mult_eq_1[OF b0] by simp}
ultimately show ?thesis by blast
qed

lemma fps_inverse_deriv':
  fixes a:: "('a :: field) fps"
  assumes a0: "a$0 \<noteq> 0"
  shows "fps_deriv (inverse a) = - fps_deriv a / a ^ 2"
  using fps_inverse_deriv[OF a0]
  unfolding power2_eq_square fps_divide_def
    fps_inverse_mult by simp

lemma inverse_mult_eq_1': assumes f0: "f$0 \<noteq> (0::'a::field)"
  shows "f * inverse f= 1"
  by (metis mult_commute inverse_mult_eq_1 f0)

lemma fps_divide_deriv:   fixes a:: "('a :: field) fps"
  assumes a0: "b$0 \<noteq> 0"
  shows "fps_deriv (a / b) = (fps_deriv a * b - a * fps_deriv b) / b ^ 2"
  using fps_inverse_deriv[OF a0]
  by (simp add: fps_divide_def ring_simps power2_eq_square fps_inverse_mult inverse_mult_eq_1'[OF a0])

subsection{* The eXtractor series X*}

lemma minus_one_power_iff: "(- (1::'a :: {comm_ring_1})) ^ n = (if even n then 1 else - 1)"
  by (induct n, auto)

definition "X = Abs_fps (\<lambda>n. if n = 1 then 1 else 0)"

lemma fps_inverse_gp': "inverse (Abs_fps(\<lambda>n. (1::'a::field)))
  = 1 - X"
  by (simp add: fps_inverse_gp fps_eq_iff X_def)

lemma X_mult_nth[simp]: "(X * (f :: ('a::semiring_1) fps)) $n = (if n = 0 then 0 else f $ (n - 1))"
proof-
  {assume n: "n \<noteq> 0"
    have fN: "finite {0 .. n}" by simp
    have "(X * f) $n = (\<Sum>i = 0..n. X $ i * f $ (n - i))" by (simp add: fps_mult_nth)
    also have "\<dots> = f $ (n - 1)"
      using n by (simp add: X_def mult_delta_left setsum_delta [OF fN])
  finally have ?thesis using n by simp }
  moreover
  {assume n: "n=0" hence ?thesis by (simp add: fps_mult_nth X_def)}
  ultimately show ?thesis by blast
qed

lemma X_mult_right_nth[simp]: "((f :: ('a::comm_semiring_1) fps) * X) $n = (if n = 0 then 0 else f $ (n - 1))"
  by (metis X_mult_nth mult_commute)

lemma X_power_iff: "X^k = Abs_fps (\<lambda>n. if n = k then (1::'a::comm_ring_1) else 0)"
proof(induct k)
  case 0 thus ?case by (simp add: X_def fps_eq_iff)
next
  case (Suc k)
  {fix m
    have "(X^Suc k) $ m = (if m = 0 then (0::'a) else (X^k) $ (m - 1))"
      by (simp add: power_Suc del: One_nat_def)
    then     have "(X^Suc k) $ m = (if m = Suc k then (1::'a) else 0)"
      using Suc.hyps by (auto cong del: if_weak_cong)}
  then show ?case by (simp add: fps_eq_iff)
qed

lemma X_power_mult_nth: "(X^k * (f :: ('a::comm_ring_1) fps)) $n = (if n < k then 0 else f $ (n - k))"
  apply (induct k arbitrary: n)
  apply (simp)
  unfolding power_Suc mult_assoc
  by (case_tac n, auto)

lemma X_power_mult_right_nth: "((f :: ('a::comm_ring_1) fps) * X^k) $n = (if n < k then 0 else f $ (n - k))"
  by (metis X_power_mult_nth mult_commute)
lemma fps_deriv_X[simp]: "fps_deriv X = 1"
  by (simp add: fps_deriv_def X_def fps_eq_iff)

lemma fps_nth_deriv_X[simp]: "fps_nth_deriv n X = (if n = 0 then X else if n=1 then 1 else 0)"
  by (cases "n", simp_all)

lemma X_nth[simp]: "X$n = (if n = 1 then 1 else 0)" by (simp add: X_def)
lemma X_power_nth[simp]: "(X^k) $n = (if n = k then 1 else (0::'a::comm_ring_1))"
  by (simp add: X_power_iff)

lemma fps_inverse_X_plus1:
  "inverse (1 + X) = Abs_fps (\<lambda>n. (- (1::'a::{field})) ^ n)" (is "_ = ?r")
proof-
  have eq: "(1 + X) * ?r = 1"
    unfolding minus_one_power_iff
    apply (auto simp add: ring_simps fps_eq_iff)
    by presburger+
  show ?thesis by (auto simp add: eq intro: fps_inverse_unique)
qed


subsection{* Integration *}
definition "fps_integral a a0 = Abs_fps (\<lambda>n. if n = 0 then a0 else (a$(n - 1) / of_nat n))"

lemma fps_deriv_fps_integral: "fps_deriv (fps_integral a (a0 :: 'a :: {field, ring_char_0})) = a"
  by (simp add: fps_integral_def fps_deriv_def fps_eq_iff field_simps del: of_nat_Suc)

lemma fps_integral_linear: "fps_integral (fps_const (a::'a::{field, ring_char_0}) * f + fps_const b * g) (a*a0 + b*b0) = fps_const a * fps_integral f a0 + fps_const b * fps_integral g b0" (is "?l = ?r")
proof-
  have "fps_deriv ?l = fps_deriv ?r" by (simp add: fps_deriv_fps_integral)
  moreover have "?l$0 = ?r$0" by (simp add: fps_integral_def)
  ultimately show ?thesis
    unfolding fps_deriv_eq_iff by auto
qed

subsection {* Composition of FPSs *}
definition fps_compose :: "('a::semiring_1) fps \<Rightarrow> 'a fps \<Rightarrow> 'a fps" (infixl "oo" 55) where
  fps_compose_def: "a oo b = Abs_fps (\<lambda>n. setsum (\<lambda>i. a$i * (b^i$n)) {0..n})"

lemma fps_compose_nth: "(a oo b)$n = setsum (\<lambda>i. a$i * (b^i$n)) {0..n}" by (simp add: fps_compose_def)

lemma fps_compose_X[simp]: "a oo X = (a :: ('a :: comm_ring_1) fps)"
  by (simp add: fps_ext fps_compose_def mult_delta_right setsum_delta')

lemma fps_const_compose[simp]:
  "fps_const (a::'a::{comm_ring_1}) oo b = fps_const (a)"
  by (simp add: fps_eq_iff fps_compose_nth mult_delta_left setsum_delta)

lemma X_fps_compose_startby0[simp]: "a$0 = 0 \<Longrightarrow> X oo a = (a :: ('a :: comm_ring_1) fps)"
  by (simp add: fps_eq_iff fps_compose_def mult_delta_left setsum_delta
                power_Suc not_le)


subsection {* Rules from Herbert Wilf's Generatingfunctionology*}

subsubsection {* Rule 1 *}
  (* {a_{n+k}}_0^infty Corresponds to (f - setsum (\<lambda>i. a_i * x^i))/x^h, for h>0*)

lemma fps_power_mult_eq_shift:
  "X^Suc k * Abs_fps (\<lambda>n. a (n + Suc k)) = Abs_fps a - setsum (\<lambda>i. fps_const (a i :: 'a:: comm_ring_1) * X^i) {0 .. k}" (is "?lhs = ?rhs")
proof-
  {fix n:: nat
    have "?lhs $ n = (if n < Suc k then 0 else a n)"
      unfolding X_power_mult_nth by auto
    also have "\<dots> = ?rhs $ n"
    proof(induct k)
      case 0 thus ?case by (simp add: fps_setsum_nth power_Suc)
    next
      case (Suc k)
      note th = Suc.hyps[symmetric]
      have "(Abs_fps a - setsum (\<lambda>i. fps_const (a i :: 'a) * X^i) {0 .. Suc k})$n = (Abs_fps a - setsum (\<lambda>i. fps_const (a i :: 'a) * X^i) {0 .. k} - fps_const (a (Suc k)) * X^ Suc k) $ n" by (simp add: ring_simps)
      also  have "\<dots> = (if n < Suc k then 0 else a n) - (fps_const (a (Suc k)) * X^ Suc k)$n"
	using th
	unfolding fps_sub_nth by simp
      also have "\<dots> = (if n < Suc (Suc k) then 0 else a n)"
	unfolding X_power_mult_right_nth
	apply (auto simp add: not_less fps_const_def)
	apply (rule cong[of a a, OF refl])
	by arith
      finally show ?case by simp
    qed
    finally have "?lhs $ n = ?rhs $ n"  .}
  then show ?thesis by (simp add: fps_eq_iff)
qed

subsubsection{* Rule 2*}

  (* We can not reach the form of Wilf, but still near to it using rewrite rules*)
  (* If f reprents {a_n} and P is a polynomial, then
        P(xD) f represents {P(n) a_n}*)

definition "XD = op * X o fps_deriv"

lemma XD_add[simp]:"XD (a + b) = XD a + XD (b :: ('a::comm_ring_1) fps)"
  by (simp add: XD_def ring_simps)

lemma XD_mult_const[simp]:"XD (fps_const (c::'a::comm_ring_1) * a) = fps_const c * XD a"
  by (simp add: XD_def ring_simps)

lemma XD_linear[simp]: "XD (fps_const c * a + fps_const d * b) = fps_const c * XD a + fps_const d * XD (b :: ('a::comm_ring_1) fps)"
  by simp

lemma XDN_linear:
  "(XD ^^ n) (fps_const c * a + fps_const d * b) = fps_const c * (XD ^^ n) a + fps_const d * (XD ^^ n) (b :: ('a::comm_ring_1) fps)"
  by (induct n, simp_all)

lemma fps_mult_X_deriv_shift: "X* fps_deriv a = Abs_fps (\<lambda>n. of_nat n* a$n)" by (simp add: fps_eq_iff)


lemma fps_mult_XD_shift:
  "(XD ^^ k) (a:: ('a::{comm_ring_1}) fps) = Abs_fps (\<lambda>n. (of_nat n ^ k) * a$n)"
  by (induct k arbitrary: a) (simp_all add: power_Suc XD_def fps_eq_iff ring_simps del: One_nat_def)

subsubsection{* Rule 3 is trivial and is given by @{text fps_times_def}*}
subsubsection{* Rule 5 --- summation and "division" by (1 - X)*}

lemma fps_divide_X_minus1_setsum_lemma:
  "a = ((1::('a::comm_ring_1) fps) - X) * Abs_fps (\<lambda>n. setsum (\<lambda>i. a $ i) {0..n})"
proof-
  let ?X = "X::('a::comm_ring_1) fps"
  let ?sa = "Abs_fps (\<lambda>n. setsum (\<lambda>i. a $ i) {0..n})"
  have th0: "\<And>i. (1 - (X::'a fps)) $ i = (if i = 0 then 1 else if i = 1 then - 1 else 0)" by simp
  {fix n:: nat
    {assume "n=0" hence "a$n = ((1 - ?X) * ?sa) $ n"
	by (simp add: fps_mult_nth)}
    moreover
    {assume n0: "n \<noteq> 0"
      then have u: "{0} \<union> ({1} \<union> {2..n}) = {0..n}" "{1}\<union>{2..n} = {1..n}"
	"{0..n - 1}\<union>{n} = {0..n}"
	apply (simp_all add: expand_set_eq) by presburger+
      have d: "{0} \<inter> ({1} \<union> {2..n}) = {}" "{1} \<inter> {2..n} = {}"
	"{0..n - 1}\<inter>{n} ={}" using n0
	by (simp_all add: expand_set_eq, presburger+)
      have f: "finite {0}" "finite {1}" "finite {2 .. n}"
	"finite {0 .. n - 1}" "finite {n}" by simp_all
    have "((1 - ?X) * ?sa) $ n = setsum (\<lambda>i. (1 - ?X)$ i * ?sa $ (n - i)) {0 .. n}"
      by (simp add: fps_mult_nth)
    also have "\<dots> = a$n" unfolding th0
      unfolding setsum_Un_disjoint[OF f(1) finite_UnI[OF f(2,3)] d(1), unfolded u(1)]
      unfolding setsum_Un_disjoint[OF f(2) f(3) d(2)]
      apply (simp)
      unfolding setsum_Un_disjoint[OF f(4,5) d(3), unfolded u(3)]
      by simp
    finally have "a$n = ((1 - ?X) * ?sa) $ n" by simp}
  ultimately have "a$n = ((1 - ?X) * ?sa) $ n" by blast}
then show ?thesis
  unfolding fps_eq_iff by blast
qed

lemma fps_divide_X_minus1_setsum:
  "a /((1::('a::field) fps) - X)  = Abs_fps (\<lambda>n. setsum (\<lambda>i. a $ i) {0..n})"
proof-
  let ?X = "1 - (X::('a::field) fps)"
  have th0: "?X $ 0 \<noteq> 0" by simp
  have "a /?X = ?X *  Abs_fps (\<lambda>n\<Colon>nat. setsum (op $ a) {0..n}) * inverse ?X"
    using fps_divide_X_minus1_setsum_lemma[of a, symmetric] th0
    by (simp add: fps_divide_def mult_assoc)
  also have "\<dots> = (inverse ?X * ?X) * Abs_fps (\<lambda>n\<Colon>nat. setsum (op $ a) {0..n}) "
    by (simp add: mult_ac)
  finally show ?thesis by (simp add: inverse_mult_eq_1[OF th0])
qed

subsubsection{* Rule 4 in its more general form: generalizes Rule 3 for an arbitrary
  finite product of FPS, also the relvant instance of powers of a FPS*}

definition "natpermute n k = {l:: nat list. length l = k \<and> foldl op + 0 l = n}"

lemma natlist_trivial_1: "natpermute n 1 = {[n]}"
  apply (auto simp add: natpermute_def)
  apply (case_tac x, auto)
  done

lemma foldl_add_start0:
  "foldl op + x xs = x + foldl op + (0::nat) xs"
  apply (induct xs arbitrary: x)
  apply simp
  unfolding foldl.simps
  apply atomize
  apply (subgoal_tac "\<forall>x\<Colon>nat. foldl op + x xs = x + foldl op + (0\<Colon>nat) xs")
  apply (erule_tac x="x + a" in allE)
  apply (erule_tac x="a" in allE)
  apply simp
  apply assumption
  done

lemma foldl_add_append: "foldl op + (x::nat) (xs@ys) = foldl op + x xs + foldl op + 0 ys"
  apply (induct ys arbitrary: x xs)
  apply auto
  apply (subst (2) foldl_add_start0)
  apply simp
  apply (subst (2) foldl_add_start0)
  by simp

lemma foldl_add_setsum: "foldl op + (x::nat) xs = x + setsum (nth xs) {0..<length xs}"
proof(induct xs arbitrary: x)
  case Nil thus ?case by simp
next
  case (Cons a as x)
  have eq: "setsum (op ! (a#as)) {1..<length (a#as)} = setsum (op ! as) {0..<length as}"
    apply (rule setsum_reindex_cong [where f=Suc])
    by (simp_all add: inj_on_def)
  have f: "finite {0}" "finite {1 ..< length (a#as)}" by simp_all
  have d: "{0} \<inter> {1..<length (a#as)} = {}" by simp
  have seq: "{0} \<union> {1..<length(a#as)} = {0 ..<length (a#as)}" by auto
  have "foldl op + x (a#as) = x + foldl op + a as "
    apply (subst foldl_add_start0)    by simp
  also have "\<dots> = x + a + setsum (op ! as) {0..<length as}" unfolding Cons.hyps by simp
  also have "\<dots> = x + setsum (op ! (a#as)) {0..<length (a#as)}"
    unfolding eq[symmetric]
    unfolding setsum_Un_disjoint[OF f d, unfolded seq]
    by simp
  finally show ?case  .
qed


lemma append_natpermute_less_eq:
  assumes h: "xs@ys \<in> natpermute n k" shows "foldl op + 0 xs \<le> n" and "foldl op + 0 ys \<le> n"
proof-
  {from h have "foldl op + 0 (xs@ ys) = n" by (simp add: natpermute_def)
    hence "foldl op + 0 xs + foldl op + 0 ys = n" unfolding foldl_add_append .}
  note th = this
  {from th show "foldl op + 0 xs \<le> n" by simp}
  {from th show "foldl op + 0 ys \<le> n" by simp}
qed

lemma natpermute_split:
  assumes mn: "h \<le> k"
  shows "natpermute n k = (\<Union>m \<in>{0..n}. {l1 @ l2 |l1 l2. l1 \<in> natpermute m h \<and> l2 \<in> natpermute (n - m) (k - h)})" (is "?L = ?R" is "?L = (\<Union>m \<in>{0..n}. ?S m)")
proof-
  {fix l assume l: "l \<in> ?R"
    from l obtain m xs ys where h: "m \<in> {0..n}" and xs: "xs \<in> natpermute m h" and ys: "ys \<in> natpermute (n - m) (k - h)"  and leq: "l = xs@ys" by blast
    from xs have xs': "foldl op + 0 xs = m" by (simp add: natpermute_def)
    from ys have ys': "foldl op + 0 ys = n - m" by (simp add: natpermute_def)
    have "l \<in> ?L" using leq xs ys h
      apply simp
      apply (clarsimp simp add: natpermute_def simp del: foldl_append)
      apply (simp add: foldl_add_append[unfolded foldl_append])
      unfolding xs' ys'
      using mn xs ys
      unfolding natpermute_def by simp}
  moreover
  {fix l assume l: "l \<in> natpermute n k"
    let ?xs = "take h l"
    let ?ys = "drop h l"
    let ?m = "foldl op + 0 ?xs"
    from l have ls: "foldl op + 0 (?xs @ ?ys) = n" by (simp add: natpermute_def)
    have xs: "?xs \<in> natpermute ?m h" using l mn by (simp add: natpermute_def)
    have ys: "?ys \<in> natpermute (n - ?m) (k - h)" using l mn ls[unfolded foldl_add_append]
      by (simp add: natpermute_def)
    from ls have m: "?m \<in> {0..n}"  unfolding foldl_add_append by simp
    from xs ys ls have "l \<in> ?R"
      apply auto
      apply (rule bexI[where x = "?m"])
      apply (rule exI[where x = "?xs"])
      apply (rule exI[where x = "?ys"])
      using ls l unfolding foldl_add_append
      by (auto simp add: natpermute_def)}
  ultimately show ?thesis by blast
qed

lemma natpermute_0: "natpermute n 0 = (if n = 0 then {[]} else {})"
  by (auto simp add: natpermute_def)
lemma natpermute_0'[simp]: "natpermute 0 k = (if k = 0 then {[]} else {replicate k 0})"
  apply (auto simp add: set_replicate_conv_if natpermute_def)
  apply (rule nth_equalityI)
  by simp_all

lemma natpermute_finite: "finite (natpermute n k)"
proof(induct k arbitrary: n)
  case 0 thus ?case
    apply (subst natpermute_split[of 0 0, simplified])
    by (simp add: natpermute_0)
next
  case (Suc k)
  then show ?case unfolding natpermute_split[of k "Suc k", simplified]
    apply -
    apply (rule finite_UN_I)
    apply simp
    unfolding One_nat_def[symmetric] natlist_trivial_1
    apply simp
    unfolding image_Collect[symmetric]
    unfolding Collect_def mem_def
    apply (rule finite_imageI)
    apply blast
    done
qed

lemma natpermute_contain_maximal:
  "{xs \<in> natpermute n (k+1). n \<in> set xs} = UNION {0 .. k} (\<lambda>i. {(replicate (k+1) 0) [i:=n]})"
  (is "?A = ?B")
proof-
  {fix xs assume H: "xs \<in> natpermute n (k+1)" and n: "n \<in> set xs"
    from n obtain i where i: "i \<in> {0.. k}" "xs!i = n" using H
      unfolding in_set_conv_nth by (auto simp add: less_Suc_eq_le natpermute_def)
    have eqs: "({0..k} - {i}) \<union> {i} = {0..k}" using i by auto
    have f: "finite({0..k} - {i})" "finite {i}" by auto
    have d: "({0..k} - {i}) \<inter> {i} = {}" using i by auto
    from H have "n = setsum (nth xs) {0..k}" apply (simp add: natpermute_def)
      unfolding foldl_add_setsum by (auto simp add: atLeastLessThanSuc_atLeastAtMost)
    also have "\<dots> = n + setsum (nth xs) ({0..k} - {i})"
      unfolding setsum_Un_disjoint[OF f d, unfolded eqs] using i by simp
    finally have zxs: "\<forall> j\<in> {0..k} - {i}. xs!j = 0" by auto
    from H have xsl: "length xs = k+1" by (simp add: natpermute_def)
    from i have i': "i < length (replicate (k+1) 0)"   "i < k+1"
      unfolding length_replicate  by arith+
    have "xs = replicate (k+1) 0 [i := n]"
      apply (rule nth_equalityI)
      unfolding xsl length_list_update length_replicate
      apply simp
      apply clarify
      unfolding nth_list_update[OF i'(1)]
      using i zxs
      by (case_tac "ia=i", auto simp del: replicate.simps)
    then have "xs \<in> ?B" using i by blast}
  moreover
  {fix i assume i: "i \<in> {0..k}"
    let ?xs = "replicate (k+1) 0 [i:=n]"
    have nxs: "n \<in> set ?xs"
      apply (rule set_update_memI) using i by simp
    have xsl: "length ?xs = k+1" by (simp only: length_replicate length_list_update)
    have "foldl op + 0 ?xs = setsum (nth ?xs) {0..<k+1}"
      unfolding foldl_add_setsum add_0 length_replicate length_list_update ..
    also have "\<dots> = setsum (\<lambda>j. if j = i then n else 0) {0..< k+1}"
      apply (rule setsum_cong2) by (simp del: replicate.simps)
    also have "\<dots> = n" using i by (simp add: setsum_delta)
    finally
    have "?xs \<in> natpermute n (k+1)" using xsl unfolding natpermute_def Collect_def mem_def
      by blast
    then have "?xs \<in> ?A"  using nxs  by blast}
  ultimately show ?thesis by auto
qed

    (* The general form *)
lemma fps_setprod_nth:
  fixes m :: nat and a :: "nat \<Rightarrow> ('a::comm_ring_1) fps"
  shows "(setprod a {0 .. m})$n = setsum (\<lambda>v. setprod (\<lambda>j. (a j) $ (v!j)) {0..m}) (natpermute n (m+1))"
  (is "?P m n")
proof(induct m arbitrary: n rule: nat_less_induct)
  fix m n assume H: "\<forall>m' < m. \<forall>n. ?P m' n"
  {assume m0: "m = 0"
    hence "?P m n" apply simp
      unfolding natlist_trivial_1[where n = n, unfolded One_nat_def] by simp}
  moreover
  {fix k assume k: "m = Suc k"
    have km: "k < m" using k by arith
    have u0: "{0 .. k} \<union> {m} = {0..m}" using k apply (simp add: expand_set_eq) by presburger
    have f0: "finite {0 .. k}" "finite {m}" by auto
    have d0: "{0 .. k} \<inter> {m} = {}" using k by auto
    have "(setprod a {0 .. m}) $ n = (setprod a {0 .. k} * a m) $ n"
      unfolding setprod_Un_disjoint[OF f0 d0, unfolded u0] by simp
    also have "\<dots> = (\<Sum>i = 0..n. (\<Sum>v\<in>natpermute i (k + 1). \<Prod>j\<in>{0..k}. a j $ v ! j) * a m $ (n - i))"
      unfolding fps_mult_nth H[rule_format, OF km] ..
    also have "\<dots> = (\<Sum>v\<in>natpermute n (m + 1). \<Prod>j\<in>{0..m}. a j $ v ! j)"
      apply (simp add: k)
      unfolding natpermute_split[of m "m + 1", simplified, of n, unfolded natlist_trivial_1[unfolded One_nat_def] k]
      apply (subst setsum_UN_disjoint)
      apply simp
      apply simp
      unfolding image_Collect[symmetric]
      apply clarsimp
      apply (rule finite_imageI)
      apply (rule natpermute_finite)
      apply (clarsimp simp add: expand_set_eq)
      apply auto
      apply (rule setsum_cong2)
      unfolding setsum_left_distrib
      apply (rule sym)
      apply (rule_tac f="\<lambda>xs. xs @[n - x]" in  setsum_reindex_cong)
      apply (simp add: inj_on_def)
      apply auto
      unfolding setprod_Un_disjoint[OF f0 d0, unfolded u0, unfolded k]
      apply (clarsimp simp add: natpermute_def nth_append)
      done
    finally have "?P m n" .}
  ultimately show "?P m n " by (cases m, auto)
qed

text{* The special form for powers *}
lemma fps_power_nth_Suc:
  fixes m :: nat and a :: "('a::comm_ring_1) fps"
  shows "(a ^ Suc m)$n = setsum (\<lambda>v. setprod (\<lambda>j. a $ (v!j)) {0..m}) (natpermute n (m+1))"
proof-
  have f: "finite {0 ..m}" by simp
  have th0: "a^Suc m = setprod (\<lambda>i. a) {0..m}" unfolding setprod_constant[OF f, of a] by simp
  show ?thesis unfolding th0 fps_setprod_nth ..
qed
lemma fps_power_nth:
  fixes m :: nat and a :: "('a::comm_ring_1) fps"
  shows "(a ^m)$n = (if m=0 then 1$n else setsum (\<lambda>v. setprod (\<lambda>j. a $ (v!j)) {0..m - 1}) (natpermute n m))"
  by (cases m, simp_all add: fps_power_nth_Suc del: power_Suc)

lemma fps_nth_power_0:
  fixes m :: nat and a :: "('a::{comm_ring_1}) fps"
  shows "(a ^m)$0 = (a$0) ^ m"
proof-
  {assume "m=0" hence ?thesis by simp}
  moreover
  {fix n assume m: "m = Suc n"
    have c: "m = card {0..n}" using m by simp
   have "(a ^m)$0 = setprod (\<lambda>i. a$0) {0..n}"
     by (simp add: m fps_power_nth del: replicate.simps power_Suc)
   also have "\<dots> = (a$0) ^ m"
     unfolding c by (rule setprod_constant, simp)
   finally have ?thesis .}
 ultimately show ?thesis by (cases m, auto)
qed

lemma fps_compose_inj_right:
  assumes a0: "a$0 = (0::'a::{idom})"
  and a1: "a$1 \<noteq> 0"
  shows "(b oo a = c oo a) \<longleftrightarrow> b = c" (is "?lhs \<longleftrightarrow>?rhs")
proof-
  {assume ?rhs then have "?lhs" by simp}
  moreover
  {assume h: ?lhs
    {fix n have "b$n = c$n"
      proof(induct n rule: nat_less_induct)
	fix n assume H: "\<forall>m<n. b$m = c$m"
	{assume n0: "n=0"
	  from h have "(b oo a)$n = (c oo a)$n" by simp
	  hence "b$n = c$n" using n0 by (simp add: fps_compose_nth)}
	moreover
	{fix n1 assume n1: "n = Suc n1"
	  have f: "finite {0 .. n1}" "finite {n}" by simp_all
	  have eq: "{0 .. n1} \<union> {n} = {0 .. n}" using n1 by auto
	  have d: "{0 .. n1} \<inter> {n} = {}" using n1 by auto
	  have seq: "(\<Sum>i = 0..n1. b $ i * a ^ i $ n) = (\<Sum>i = 0..n1. c $ i * a ^ i $ n)"
	    apply (rule setsum_cong2)
	    using H n1 by auto
	  have th0: "(b oo a) $n = (\<Sum>i = 0..n1. c $ i * a ^ i $ n) + b$n * (a$1)^n"
	    unfolding fps_compose_nth setsum_Un_disjoint[OF f d, unfolded eq] seq
	    using startsby_zero_power_nth_same[OF a0]
	    by simp
	  have th1: "(c oo a) $n = (\<Sum>i = 0..n1. c $ i * a ^ i $ n) + c$n * (a$1)^n"
	    unfolding fps_compose_nth setsum_Un_disjoint[OF f d, unfolded eq]
	    using startsby_zero_power_nth_same[OF a0]
	    by simp
	  from h[unfolded fps_eq_iff, rule_format, of n] th0 th1 a1
	  have "b$n = c$n" by auto}
	ultimately show "b$n = c$n" by (cases n, auto)
      qed}
    then have ?rhs by (simp add: fps_eq_iff)}
  ultimately show ?thesis by blast
qed


subsection {* Radicals *}

declare setprod_cong[fundef_cong]
function radical :: "(nat \<Rightarrow> 'a \<Rightarrow> 'a) \<Rightarrow> nat \<Rightarrow> ('a::{field}) fps \<Rightarrow> nat \<Rightarrow> 'a" where
  "radical r 0 a 0 = 1"
| "radical r 0 a (Suc n) = 0"
| "radical r (Suc k) a 0 = r (Suc k) (a$0)"
| "radical r (Suc k) a (Suc n) = (a$ Suc n - setsum (\<lambda>xs. setprod (\<lambda>j. radical r (Suc k) a (xs ! j)) {0..k}) {xs. xs \<in> natpermute (Suc n) (Suc k) \<and> Suc n \<notin> set xs}) / (of_nat (Suc k) * (radical r (Suc k) a 0)^k)"
by pat_completeness auto

termination radical
proof
  let ?R = "measure (\<lambda>(r, k, a, n). n)"
  {
    show "wf ?R" by auto}
  {fix r k a n xs i
    assume xs: "xs \<in> {xs \<in> natpermute (Suc n) (Suc k). Suc n \<notin> set xs}" and i: "i \<in> {0..k}"
    {assume c: "Suc n \<le> xs ! i"
      from xs i have "xs !i \<noteq> Suc n" by (auto simp add: in_set_conv_nth natpermute_def)
      with c have c': "Suc n < xs!i" by arith
      have fths: "finite {0 ..< i}" "finite {i}" "finite {i+1..<Suc k}" by simp_all
      have d: "{0 ..< i} \<inter> ({i} \<union> {i+1 ..< Suc k}) = {}" "{i} \<inter> {i+1..< Suc k} = {}" by auto
      have eqs: "{0..<Suc k} = {0 ..< i} \<union> ({i} \<union> {i+1 ..< Suc k})" using i by auto
      from xs have "Suc n = foldl op + 0 xs" by (simp add: natpermute_def)
      also have "\<dots> = setsum (nth xs) {0..<Suc k}" unfolding foldl_add_setsum using xs
	by (simp add: natpermute_def)
      also have "\<dots> = xs!i + setsum (nth xs) {0..<i} + setsum (nth xs) {i+1..<Suc k}"
	unfolding eqs  setsum_Un_disjoint[OF fths(1) finite_UnI[OF fths(2,3)] d(1)]
	unfolding setsum_Un_disjoint[OF fths(2) fths(3) d(2)]
	by simp
      finally have False using c' by simp}
    then show "((r,Suc k,a,xs!i), r, Suc k, a, Suc n) \<in> ?R"
      apply auto by (metis not_less)}
  {fix r k a n
    show "((r,Suc k, a, 0),r, Suc k, a, Suc n) \<in> ?R" by simp}
qed

definition "fps_radical r n a = Abs_fps (radical r n a)"

lemma fps_radical0[simp]: "fps_radical r 0 a = 1"
  apply (auto simp add: fps_eq_iff fps_radical_def)  by (case_tac n, auto)

lemma fps_radical_nth_0[simp]: "fps_radical r n a $ 0 = (if n=0 then 1 else r n (a$0))"
  by (cases n, simp_all add: fps_radical_def)

lemma fps_radical_power_nth[simp]:
  assumes r: "(r k (a$0)) ^ k = a$0"
  shows "fps_radical r k a ^ k $ 0 = (if k = 0 then 1 else a$0)"
proof-
  {assume "k=0" hence ?thesis by simp }
  moreover
  {fix h assume h: "k = Suc h"
    have fh: "finite {0..h}" by simp
    have eq1: "fps_radical r k a ^ k $ 0 = (\<Prod>j\<in>{0..h}. fps_radical r k a $ (replicate k 0) ! j)"
      unfolding fps_power_nth h by simp
    also have "\<dots> = (\<Prod>j\<in>{0..h}. r k (a$0))"
      apply (rule setprod_cong)
      apply simp
      using h
      apply (subgoal_tac "replicate k (0::nat) ! x = 0")
      by (auto intro: nth_replicate simp del: replicate.simps)
    also have "\<dots> = a$0"
      unfolding setprod_constant[OF fh] using r by (simp add: h)
    finally have ?thesis using h by simp}
  ultimately show ?thesis by (cases k, auto)
qed

lemma natpermute_max_card: assumes n0: "n\<noteq>0"
  shows "card {xs \<in> natpermute n (k+1). n \<in> set xs} = k+1"
  unfolding natpermute_contain_maximal
proof-
  let ?A= "\<lambda>i. {replicate (k + 1) 0[i := n]}"
  let ?K = "{0 ..k}"
  have fK: "finite ?K" by simp
  have fAK: "\<forall>i\<in>?K. finite (?A i)" by auto
  have d: "\<forall>i\<in> ?K. \<forall>j\<in> ?K. i \<noteq> j \<longrightarrow> {replicate (k + 1) 0[i := n]} \<inter> {replicate (k + 1) 0[j := n]} = {}"
  proof(clarify)
    fix i j assume i: "i \<in> ?K" and j: "j\<in> ?K" and ij: "i\<noteq>j"
    {assume eq: "replicate (k+1) 0 [i:=n] = replicate (k+1) 0 [j:= n]"
      have "(replicate (k+1) 0 [i:=n] ! i) = n" using i by (simp del: replicate.simps)
      moreover
      have "(replicate (k+1) 0 [j:=n] ! i) = 0" using i ij by (simp del: replicate.simps)
      ultimately have False using eq n0 by (simp del: replicate.simps)}
    then show "{replicate (k + 1) 0[i := n]} \<inter> {replicate (k + 1) 0[j := n]} = {}"
      by auto
  qed
  from card_UN_disjoint[OF fK fAK d]
  show "card (\<Union>i\<in>{0..k}. {replicate (k + 1) 0[i := n]}) = k+1" by simp
qed

lemma power_radical:
  fixes a:: "'a ::{field, ring_char_0} fps"
  assumes r0: "(r (Suc k) (a$0)) ^ Suc k = a$0" and a0: "a$0 \<noteq> 0"
  shows "(fps_radical r (Suc k) a) ^ (Suc k) = a"
proof-
  let ?r = "fps_radical r (Suc k) a"
  from a0 r0 have r00: "r (Suc k) (a$0) \<noteq> 0" by auto
  {fix z have "?r ^ Suc k $ z = a$z"
    proof(induct z rule: nat_less_induct)
      fix n assume H: "\<forall>m<n. ?r ^ Suc k $ m = a$m"
      {assume "n = 0" hence "?r ^ Suc k $ n = a $n"
	  using fps_radical_power_nth[of r "Suc k" a, OF r0] by simp}
      moreover
      {fix n1 assume n1: "n = Suc n1"
	have fK: "finite {0..k}" by simp
	have nz: "n \<noteq> 0" using n1 by arith
	let ?Pnk = "natpermute n (k + 1)"
	let ?Pnkn = "{xs \<in> ?Pnk. n \<in> set xs}"
	let ?Pnknn = "{xs \<in> ?Pnk. n \<notin> set xs}"
	have eq: "?Pnkn \<union> ?Pnknn = ?Pnk" by blast
	have d: "?Pnkn \<inter> ?Pnknn = {}" by blast
	have f: "finite ?Pnkn" "finite ?Pnknn"
	  using finite_Un[of ?Pnkn ?Pnknn, unfolded eq]
	  by (metis natpermute_finite)+
	let ?f = "\<lambda>v. \<Prod>j\<in>{0..k}. ?r $ v ! j"
	have "setsum ?f ?Pnkn = setsum (\<lambda>v. ?r $ n * r (Suc k) (a $ 0) ^ k) ?Pnkn"
	proof(rule setsum_cong2)
	  fix v assume v: "v \<in> {xs \<in> natpermute n (k + 1). n \<in> set xs}"
	  let ?ths = "(\<Prod>j\<in>{0..k}. fps_radical r (Suc k) a $ v ! j) = fps_radical r (Suc k) a $ n * r (Suc k) (a $ 0) ^ k"
	  from v obtain i where i: "i \<in> {0..k}" "v = replicate (k+1) 0 [i:= n]"
	    unfolding natpermute_contain_maximal by auto
	  have "(\<Prod>j\<in>{0..k}. fps_radical r (Suc k) a $ v ! j) = (\<Prod>j\<in>{0..k}. if j = i then fps_radical r (Suc k) a $ n else r (Suc k) (a$0))"
	    apply (rule setprod_cong, simp)
	    using i r0 by (simp del: replicate.simps)
	  also have "\<dots> = (fps_radical r (Suc k) a $ n) * r (Suc k) (a$0) ^ k"
	    unfolding setprod_gen_delta[OF fK] using i r0 by simp
	  finally show ?ths .
	qed
	then have "setsum ?f ?Pnkn = of_nat (k+1) * ?r $ n * r (Suc k) (a $ 0) ^ k"
	  by (simp add: natpermute_max_card[OF nz, simplified])
	also have "\<dots> = a$n - setsum ?f ?Pnknn"
	  unfolding n1 using r00 a0 by (simp add: field_simps fps_radical_def del: of_nat_Suc )
	finally have fn: "setsum ?f ?Pnkn = a$n - setsum ?f ?Pnknn" .
	have "(?r ^ Suc k)$n = setsum ?f ?Pnkn + setsum ?f ?Pnknn"
	  unfolding fps_power_nth_Suc setsum_Un_disjoint[OF f d, unfolded eq] ..
	also have "\<dots> = a$n" unfolding fn by simp
	finally have "?r ^ Suc k $ n = a $n" .}
      ultimately  show "?r ^ Suc k $ n = a $n" by (cases n, auto)
  qed }
  then show ?thesis by (simp add: fps_eq_iff)
qed

lemma eq_divide_imp': assumes c0: "(c::'a::field) ~= 0" and eq: "a * c = b"
  shows "a = b / c"
proof-
  from eq have "a * c * inverse c = b * inverse c" by simp
  hence "a * (inverse c * c) = b/c" by (simp only: field_simps divide_inverse)
  then show "a = b/c" unfolding  field_inverse[OF c0] by simp
qed

lemma radical_unique:
  assumes r0: "(r (Suc k) (b$0)) ^ Suc k = b$0"
  and a0: "r (Suc k) (b$0 ::'a::{field, ring_char_0}) = a$0" and b0: "b$0 \<noteq> 0"
  shows "a^(Suc k) = b \<longleftrightarrow> a = fps_radical r (Suc k) b"
proof-
  let ?r = "fps_radical r (Suc k) b"
  have r00: "r (Suc k) (b$0) \<noteq> 0" using b0 r0 by auto
  {assume H: "a = ?r"
    from H have "a^Suc k = b" using power_radical[of r k, OF r0 b0] by simp}
  moreover
  {assume H: "a^Suc k = b"
    (* Generally a$0 would need to be the k+1 st root of b$0 *)
    have ceq: "card {0..k} = Suc k" by simp
    have fk: "finite {0..k}" by simp
    from a0 have a0r0: "a$0 = ?r$0" by simp
    {fix n have "a $ n = ?r $ n"
      proof(induct n rule: nat_less_induct)
	fix n assume h: "\<forall>m<n. a$m = ?r $m"
	{assume "n = 0" hence "a$n = ?r $n" using a0 by simp }
	moreover
	{fix n1 assume n1: "n = Suc n1"
	  have fK: "finite {0..k}" by simp
	have nz: "n \<noteq> 0" using n1 by arith
	let ?Pnk = "natpermute n (Suc k)"
	let ?Pnkn = "{xs \<in> ?Pnk. n \<in> set xs}"
	let ?Pnknn = "{xs \<in> ?Pnk. n \<notin> set xs}"
	have eq: "?Pnkn \<union> ?Pnknn = ?Pnk" by blast
	have d: "?Pnkn \<inter> ?Pnknn = {}" by blast
	have f: "finite ?Pnkn" "finite ?Pnknn"
	  using finite_Un[of ?Pnkn ?Pnknn, unfolded eq]
	  by (metis natpermute_finite)+
	let ?f = "\<lambda>v. \<Prod>j\<in>{0..k}. ?r $ v ! j"
	let ?g = "\<lambda>v. \<Prod>j\<in>{0..k}. a $ v ! j"
	have "setsum ?g ?Pnkn = setsum (\<lambda>v. a $ n * (?r$0)^k) ?Pnkn"
	proof(rule setsum_cong2)
	  fix v assume v: "v \<in> {xs \<in> natpermute n (Suc k). n \<in> set xs}"
	  let ?ths = "(\<Prod>j\<in>{0..k}. a $ v ! j) = a $ n * (?r$0)^k"
	  from v obtain i where i: "i \<in> {0..k}" "v = replicate (k+1) 0 [i:= n]"
	    unfolding Suc_plus1 natpermute_contain_maximal by (auto simp del: replicate.simps)
	  have "(\<Prod>j\<in>{0..k}. a $ v ! j) = (\<Prod>j\<in>{0..k}. if j = i then a $ n else r (Suc k) (b$0))"
	    apply (rule setprod_cong, simp)
	    using i a0 by (simp del: replicate.simps)
	  also have "\<dots> = a $ n * (?r $ 0)^k"
	    unfolding  setprod_gen_delta[OF fK] using i by simp
	  finally show ?ths .
	qed
	then have th0: "setsum ?g ?Pnkn = of_nat (k+1) * a $ n * (?r $ 0)^k"
	  by (simp add: natpermute_max_card[OF nz, simplified])
	have th1: "setsum ?g ?Pnknn = setsum ?f ?Pnknn"
	proof (rule setsum_cong2, rule setprod_cong, simp)
	  fix xs i assume xs: "xs \<in> ?Pnknn" and i: "i \<in> {0..k}"
	  {assume c: "n \<le> xs ! i"
	    from xs i have "xs !i \<noteq> n" by (auto simp add: in_set_conv_nth natpermute_def)
	    with c have c': "n < xs!i" by arith
	    have fths: "finite {0 ..< i}" "finite {i}" "finite {i+1..<Suc k}" by simp_all
	    have d: "{0 ..< i} \<inter> ({i} \<union> {i+1 ..< Suc k}) = {}" "{i} \<inter> {i+1..< Suc k} = {}" by auto
	    have eqs: "{0..<Suc k} = {0 ..< i} \<union> ({i} \<union> {i+1 ..< Suc k})" using i by auto
	    from xs have "n = foldl op + 0 xs" by (simp add: natpermute_def)
	    also have "\<dots> = setsum (nth xs) {0..<Suc k}" unfolding foldl_add_setsum using xs
	      by (simp add: natpermute_def)
	    also have "\<dots> = xs!i + setsum (nth xs) {0..<i} + setsum (nth xs) {i+1..<Suc k}"
	      unfolding eqs  setsum_Un_disjoint[OF fths(1) finite_UnI[OF fths(2,3)] d(1)]
	      unfolding setsum_Un_disjoint[OF fths(2) fths(3) d(2)]
	      by simp
	    finally have False using c' by simp}
	  then have thn: "xs!i < n" by arith
	  from h[rule_format, OF thn]
	  show "a$(xs !i) = ?r$(xs!i)" .
	qed
	have th00: "\<And>(x::'a). of_nat (Suc k) * (x * inverse (of_nat (Suc k))) = x"
	  by (simp add: field_simps del: of_nat_Suc)
	from H have "b$n = a^Suc k $ n" by (simp add: fps_eq_iff)
	also have "a ^ Suc k$n = setsum ?g ?Pnkn + setsum ?g ?Pnknn"
	  unfolding fps_power_nth_Suc
	  using setsum_Un_disjoint[OF f d, unfolded Suc_plus1[symmetric],
	    unfolded eq, of ?g] by simp
	also have "\<dots> = of_nat (k+1) * a $ n * (?r $ 0)^k + setsum ?f ?Pnknn" unfolding th0 th1 ..
	finally have "of_nat (k+1) * a $ n * (?r $ 0)^k = b$n - setsum ?f ?Pnknn" by simp
	then have "a$n = (b$n - setsum ?f ?Pnknn) / (of_nat (k+1) * (?r $ 0)^k)"
	  apply -
	  apply (rule eq_divide_imp')
	  using r00
	  apply (simp del: of_nat_Suc)
	  by (simp add: mult_ac)
	then have "a$n = ?r $n"
	  apply (simp del: of_nat_Suc)
	  unfolding fps_radical_def n1
	  by (simp add: field_simps n1 th00 del: of_nat_Suc)}
	ultimately show "a$n = ?r $ n" by (cases n, auto)
      qed}
    then have "a = ?r" by (simp add: fps_eq_iff)}
  ultimately show ?thesis by blast
qed


lemma radical_power:
  assumes r0: "r (Suc k) ((a$0) ^ Suc k) = a$0"
  and a0: "(a$0 ::'a::{field, ring_char_0}) \<noteq> 0"
  shows "(fps_radical r (Suc k) (a ^ Suc k)) = a"
proof-
  let ?ak = "a^ Suc k"
  have ak0: "?ak $ 0 = (a$0) ^ Suc k" by (simp add: fps_nth_power_0 del: power_Suc)
  from r0 have th0: "r (Suc k) (a ^ Suc k $ 0) ^ Suc k = a ^ Suc k $ 0" using ak0 by auto
  from r0 ak0 have th1: "r (Suc k) (a ^ Suc k $ 0) = a $ 0" by auto
  from ak0 a0 have ak00: "?ak $ 0 \<noteq>0 " by auto
  from radical_unique[of r k ?ak a, OF th0 th1 ak00] show ?thesis by metis
qed

lemma fps_deriv_radical:
  fixes a:: "'a ::{field, ring_char_0} fps"
  assumes r0: "(r (Suc k) (a$0)) ^ Suc k = a$0" and a0: "a$0 \<noteq> 0"
  shows "fps_deriv (fps_radical r (Suc k) a) = fps_deriv a / (fps_const (of_nat (Suc k)) * (fps_radical r (Suc k) a) ^ k)"
proof-
  let ?r= "fps_radical r (Suc k) a"
  let ?w = "(fps_const (of_nat (Suc k)) * ?r ^ k)"
  from a0 r0 have r0': "r (Suc k) (a$0) \<noteq> 0" by auto
  from r0' have w0: "?w $ 0 \<noteq> 0" by (simp del: of_nat_Suc)
  note th0 = inverse_mult_eq_1[OF w0]
  let ?iw = "inverse ?w"
  from power_radical[of r, OF r0 a0]
  have "fps_deriv (?r ^ Suc k) = fps_deriv a" by simp
  hence "fps_deriv ?r * ?w = fps_deriv a"
    by (simp add: fps_deriv_power mult_ac del: power_Suc)
  hence "?iw * fps_deriv ?r * ?w = ?iw * fps_deriv a" by simp
  hence "fps_deriv ?r * (?iw * ?w) = fps_deriv a / ?w"
    by (simp add: fps_divide_def)
  then show ?thesis unfolding th0 by simp
qed

lemma radical_mult_distrib:
  fixes a:: "'a ::{field, ring_char_0} fps"
  assumes
  ra0: "r (k) (a $ 0) ^ k = a $ 0"
  and rb0: "r (k) (b $ 0) ^ k = b $ 0"
  and r0': "r (k) ((a * b) $ 0) = r (k) (a $ 0) * r (k) (b $ 0)"
  and a0: "a$0 \<noteq> 0"
  and b0: "b$0 \<noteq> 0"
  shows "fps_radical r (k) (a*b) = fps_radical r (k) a * fps_radical r (k) (b)"
proof-
  from r0' have r0: "(r (k) ((a*b)$0)) ^ k = (a*b)$0"
    by (simp add: fps_mult_nth ra0 rb0 power_mult_distrib)
  {assume "k=0" hence ?thesis by simp}
  moreover
  {fix h assume k: "k = Suc h"
  let ?ra = "fps_radical r (Suc h) a"
  let ?rb = "fps_radical r (Suc h) b"
  have th0: "r (Suc h) ((a * b) $ 0) = (fps_radical r (Suc h) a * fps_radical r (Suc h) b) $ 0"
    using r0' k by (simp add: fps_mult_nth)
  have ab0: "(a*b) $ 0 \<noteq> 0" using a0 b0 by (simp add: fps_mult_nth)
  from radical_unique[of r h "a*b" "fps_radical r (Suc h) a * fps_radical r (Suc h) b", OF r0[unfolded k] th0 ab0, symmetric]
    power_radical[of r, OF ra0[unfolded k] a0] power_radical[of r, OF rb0[unfolded k] b0] k
  have ?thesis by (auto simp add: power_mult_distrib simp del: power_Suc)}
ultimately show ?thesis by (cases k, auto)
qed

lemma radical_inverse:
  fixes a:: "'a ::{field, ring_char_0} fps"
  assumes
  ra0: "r (k) (a $ 0) ^ k = a $ 0"
  and ria0: "r (k) (inverse (a $ 0)) = inverse (r (k) (a $ 0))"
  and r1: "(r (k) 1) = 1"
  and a0: "a$0 \<noteq> 0"
  shows "fps_radical r (k) (inverse a) = inverse (fps_radical r (k) a)"
proof-
  {assume "k=0" then have ?thesis by simp}
  moreover
  {fix h assume k[simp]: "k = Suc h"
    let ?ra = "fps_radical r (Suc h) a"
    let ?ria = "fps_radical r (Suc h) (inverse a)"
    from ra0 a0 have th00: "r (Suc h) (a$0) \<noteq> 0" by auto
    have ria0': "r (Suc h) (inverse a $ 0) ^ Suc h = inverse a$0"
    using ria0 ra0 a0
    by (simp add: fps_inverse_def  nonzero_power_inverse[OF th00, symmetric]
             del: power_Suc)
  from inverse_mult_eq_1[OF a0] have th0: "a * inverse a = 1"
    by (simp add: mult_commute)
  from radical_unique[where a=1 and b=1 and r=r and k=h, simplified, OF r1[unfolded k]]
  have th01: "fps_radical r (Suc h) 1 = 1" .
  have th1: "r (Suc h) ((a * inverse a) $ 0) ^ Suc h = (a * inverse a) $ 0"
    "r (Suc h) ((a * inverse a) $ 0) =
r (Suc h) (a $ 0) * r (Suc h) (inverse a $ 0)"
    using r1 unfolding th0  apply (simp_all add: ria0[symmetric])
    apply (simp add: fps_inverse_def a0)
    unfolding ria0[unfolded k]
    using th00 by simp
  from nonzero_imp_inverse_nonzero[OF a0] a0
  have th2: "inverse a $ 0 \<noteq> 0" by (simp add: fps_inverse_def)
  from radical_mult_distrib[of r "Suc h" a "inverse a", OF ra0[unfolded k] ria0' th1(2) a0 th2]
  have th3: "?ra * ?ria = 1" unfolding th0 th01 by simp
  from th00 have ra0: "?ra $ 0 \<noteq> 0" by simp
  from fps_inverse_unique[OF ra0 th3] have ?thesis by simp}
ultimately show ?thesis by (cases k, auto)
qed

lemma fps_divide_inverse: "(a::('a::field) fps) / b = a * inverse b"
  by (simp add: fps_divide_def)

lemma radical_divide:
  fixes a:: "'a ::{field, ring_char_0} fps"
  assumes
      ra0: "r k (a $ 0) ^ k = a $ 0"
  and rb0: "r k (b $ 0) ^ k = b $ 0"
  and r1: "r k 1 = 1"
  and rb0': "r k (inverse (b $ 0)) = inverse (r k (b $ 0))"
  and raib': "r k (a$0 / (b$0)) = r k (a$0) / r k (b$0)"
  and a0: "a$0 \<noteq> 0"
  and b0: "b$0 \<noteq> 0"
  shows "fps_radical r k (a/b) = fps_radical r k a / fps_radical r k b"
proof-
  from raib'
  have raib: "r k (a$0 / (b$0)) = r k (a$0) * r k (inverse (b$0))"
    by (simp add: divide_inverse rb0'[symmetric])

  {assume "k=0" hence ?thesis by (simp add: fps_divide_def)}
  moreover
  {assume k0: "k\<noteq> 0"
    from b0 k0 rb0 have rbn0: "r k (b $0) \<noteq> 0"
      by (auto simp add: power_0_left)

    from rb0 rb0' have rib0: "(r k (inverse (b $ 0)))^k = inverse (b$0)"
    by (simp add: nonzero_power_inverse[OF rbn0, symmetric])
  from rib0 have th0: "r k (inverse b $ 0) ^ k = inverse b $ 0"
    by (simp add:fps_inverse_def b0)
  from raib
  have th1: "r k ((a * inverse b) $ 0) = r k (a $ 0) * r k (inverse b $ 0)"
    by (simp add: divide_inverse fps_inverse_def  b0 fps_mult_nth)
  from nonzero_imp_inverse_nonzero[OF b0] b0 have th2: "inverse b $ 0 \<noteq> 0"
    by (simp add: fps_inverse_def)
  from radical_mult_distrib[of r k a "inverse b", OF ra0 th0 th1 a0 th2]
  have th: "fps_radical r k (a/b) = fps_radical r k a * fps_radical r k (inverse b)"
    by (simp add: fps_divide_def)
  with radical_inverse[of r k b, OF rb0 rb0' r1 b0]
  have ?thesis by (simp add: fps_divide_def)}
ultimately show ?thesis by blast
qed

subsection{* Derivative of composition *}

lemma fps_compose_deriv:
  fixes a:: "('a::idom) fps"
  assumes b0: "b$0 = 0"
  shows "fps_deriv (a oo b) = ((fps_deriv a) oo b) * (fps_deriv b)"
proof-
  {fix n
    have "(fps_deriv (a oo b))$n = setsum (\<lambda>i. a $ i * (fps_deriv (b^i))$n) {0.. Suc n}"
      by (simp add: fps_compose_def ring_simps setsum_right_distrib del: of_nat_Suc)
    also have "\<dots> = setsum (\<lambda>i. a$i * ((fps_const (of_nat i)) * (fps_deriv b * (b^(i - 1))))$n) {0.. Suc n}"
      by (simp add: ring_simps fps_deriv_power del: fps_mult_left_const_nth of_nat_Suc)
  also have "\<dots> = setsum (\<lambda>i. of_nat i * a$i * (((b^(i - 1)) * fps_deriv b))$n) {0.. Suc n}"
    unfolding fps_mult_left_const_nth  by (simp add: ring_simps)
  also have "\<dots> = setsum (\<lambda>i. of_nat i * a$i * (setsum (\<lambda>j. (b^ (i - 1))$j * (fps_deriv b)$(n - j)) {0..n})) {0.. Suc n}"
    unfolding fps_mult_nth ..
  also have "\<dots> = setsum (\<lambda>i. of_nat i * a$i * (setsum (\<lambda>j. (b^ (i - 1))$j * (fps_deriv b)$(n - j)) {0..n})) {1.. Suc n}"
    apply (rule setsum_mono_zero_right)
    apply (auto simp add: mult_delta_left setsum_delta not_le)
    done
  also have "\<dots> = setsum (\<lambda>i. of_nat (i + 1) * a$(i+1) * (setsum (\<lambda>j. (b^ i)$j * of_nat (n - j + 1) * b$(n - j + 1)) {0..n})) {0.. n}"
    unfolding fps_deriv_nth
    apply (rule setsum_reindex_cong[where f="Suc"])
    by (auto simp add: mult_assoc)
  finally have th0: "(fps_deriv (a oo b))$n = setsum (\<lambda>i. of_nat (i + 1) * a$(i+1) * (setsum (\<lambda>j. (b^ i)$j * of_nat (n - j + 1) * b$(n - j + 1)) {0..n})) {0.. n}" .

  have "(((fps_deriv a) oo b) * (fps_deriv b))$n = setsum (\<lambda>i. (fps_deriv b)$ (n - i) * ((fps_deriv a) oo b)$i) {0..n}"
    unfolding fps_mult_nth by (simp add: mult_ac)
  also have "\<dots> = setsum (\<lambda>i. setsum (\<lambda>j. of_nat (n - i +1) * b$(n - i + 1) * of_nat (j + 1) * a$(j+1) * (b^j)$i) {0..n}) {0..n}"
    unfolding fps_deriv_nth fps_compose_nth setsum_right_distrib mult_assoc
    apply (rule setsum_cong2)
    apply (rule setsum_mono_zero_left)
    apply (simp_all add: subset_eq)
    apply clarify
    apply (subgoal_tac "b^i$x = 0")
    apply simp
    apply (rule startsby_zero_power_prefix[OF b0, rule_format])
    by simp
  also have "\<dots> = setsum (\<lambda>i. of_nat (i + 1) * a$(i+1) * (setsum (\<lambda>j. (b^ i)$j * of_nat (n - j + 1) * b$(n - j + 1)) {0..n})) {0.. n}"
    unfolding setsum_right_distrib
    apply (subst setsum_commute)
    by ((rule setsum_cong2)+) simp
  finally have "(fps_deriv (a oo b))$n = (((fps_deriv a) oo b) * (fps_deriv b)) $n"
    unfolding th0 by simp}
then show ?thesis by (simp add: fps_eq_iff)
qed

lemma fps_mult_X_plus_1_nth:
  "((1+X)*a) $n = (if n = 0 then (a$n :: 'a::comm_ring_1) else a$n + a$(n - 1))"
proof-
  {assume "n = 0" hence ?thesis by (simp add: fps_mult_nth )}
  moreover
  {fix m assume m: "n = Suc m"
    have "((1+X)*a) $n = setsum (\<lambda>i. (1+X)$i * a$(n-i)) {0..n}"
      by (simp add: fps_mult_nth)
    also have "\<dots> = setsum (\<lambda>i. (1+X)$i * a$(n-i)) {0.. 1}"
      unfolding m
      apply (rule setsum_mono_zero_right)
      by (auto simp add: )
    also have "\<dots> = (if n = 0 then (a$n :: 'a::comm_ring_1) else a$n + a$(n - 1))"
      unfolding m
      by (simp add: )
    finally have ?thesis .}
  ultimately show ?thesis by (cases n, auto)
qed

subsection{* Finite FPS (i.e. polynomials) and X *}
lemma fps_poly_sum_X:
  assumes z: "\<forall>i > n. a$i = (0::'a::comm_ring_1)"
  shows "a = setsum (\<lambda>i. fps_const (a$i) * X^i) {0..n}" (is "a = ?r")
proof-
  {fix i
    have "a$i = ?r$i"
      unfolding fps_setsum_nth fps_mult_left_const_nth X_power_nth
      by (simp add: mult_delta_right setsum_delta' z)
  }
  then show ?thesis unfolding fps_eq_iff by blast
qed

subsection{* Compositional inverses *}


fun compinv :: "'a fps \<Rightarrow> nat \<Rightarrow> 'a::{field}" where
  "compinv a 0 = X$0"
| "compinv a (Suc n) = (X$ Suc n - setsum (\<lambda>i. (compinv a i) * (a^i)$Suc n) {0 .. n}) / (a$1) ^ Suc n"

definition "fps_inv a = Abs_fps (compinv a)"

lemma fps_inv: assumes a0: "a$0 = 0" and a1: "a$1 \<noteq> 0"
  shows "fps_inv a oo a = X"
proof-
  let ?i = "fps_inv a oo a"
  {fix n
    have "?i $n = X$n"
    proof(induct n rule: nat_less_induct)
      fix n assume h: "\<forall>m<n. ?i$m = X$m"
      {assume "n=0" hence "?i $n = X$n" using a0
	  by (simp add: fps_compose_nth fps_inv_def)}
      moreover
      {fix n1 assume n1: "n = Suc n1"
	have "?i $ n = setsum (\<lambda>i. (fps_inv a $ i) * (a^i)$n) {0 .. n1} + fps_inv a $ Suc n1 * (a $ 1)^ Suc n1"
	  by (simp add: fps_compose_nth n1 startsby_zero_power_nth_same[OF a0]
                   del: power_Suc)
	also have "\<dots> = setsum (\<lambda>i. (fps_inv a $ i) * (a^i)$n) {0 .. n1} + (X$ Suc n1 - setsum (\<lambda>i. (fps_inv a $ i) * (a^i)$n) {0 .. n1})"
	  using a0 a1 n1 by (simp add: fps_inv_def)
	also have "\<dots> = X$n" using n1 by simp
	finally have "?i $ n = X$n" .}
      ultimately show "?i $ n = X$n" by (cases n, auto)
    qed}
  then show ?thesis by (simp add: fps_eq_iff)
qed


fun gcompinv :: "'a fps \<Rightarrow> 'a fps \<Rightarrow> nat \<Rightarrow> 'a::{field}" where
  "gcompinv b a 0 = b$0"
| "gcompinv b a (Suc n) = (b$ Suc n - setsum (\<lambda>i. (gcompinv b a i) * (a^i)$Suc n) {0 .. n}) / (a$1) ^ Suc n"

definition "fps_ginv b a = Abs_fps (gcompinv b a)"

lemma fps_ginv: assumes a0: "a$0 = 0" and a1: "a$1 \<noteq> 0"
  shows "fps_ginv b a oo a = b"
proof-
  let ?i = "fps_ginv b a oo a"
  {fix n
    have "?i $n = b$n"
    proof(induct n rule: nat_less_induct)
      fix n assume h: "\<forall>m<n. ?i$m = b$m"
      {assume "n=0" hence "?i $n = b$n" using a0
	  by (simp add: fps_compose_nth fps_ginv_def)}
      moreover
      {fix n1 assume n1: "n = Suc n1"
	have "?i $ n = setsum (\<lambda>i. (fps_ginv b a $ i) * (a^i)$n) {0 .. n1} + fps_ginv b a $ Suc n1 * (a $ 1)^ Suc n1"
	  by (simp add: fps_compose_nth n1 startsby_zero_power_nth_same[OF a0]
                   del: power_Suc)
	also have "\<dots> = setsum (\<lambda>i. (fps_ginv b a $ i) * (a^i)$n) {0 .. n1} + (b$ Suc n1 - setsum (\<lambda>i. (fps_ginv b a $ i) * (a^i)$n) {0 .. n1})"
	  using a0 a1 n1 by (simp add: fps_ginv_def)
	also have "\<dots> = b$n" using n1 by simp
	finally have "?i $ n = b$n" .}
      ultimately show "?i $ n = b$n" by (cases n, auto)
    qed}
  then show ?thesis by (simp add: fps_eq_iff)
qed

lemma fps_inv_ginv: "fps_inv = fps_ginv X"
  apply (auto simp add: expand_fun_eq fps_eq_iff fps_inv_def fps_ginv_def)
  apply (induct_tac n rule: nat_less_induct, auto)
  apply (case_tac na)
  apply simp
  apply simp
  done

lemma fps_compose_1[simp]: "1 oo a = 1"
  by (simp add: fps_eq_iff fps_compose_nth mult_delta_left setsum_delta)

lemma fps_compose_0[simp]: "0 oo a = 0"
  by (simp add: fps_eq_iff fps_compose_nth)

lemma fps_compose_0_right[simp]: "a oo 0 = fps_const (a$0)"
  by (auto simp add: fps_eq_iff fps_compose_nth power_0_left setsum_0')

lemma fps_compose_add_distrib: "(a + b) oo c = (a oo c) + (b oo c)"
  by (simp add: fps_eq_iff fps_compose_nth ring_simps setsum_addf)

lemma fps_compose_setsum_distrib: "(setsum f S) oo a = setsum (\<lambda>i. f i oo a) S"
proof-
  {assume "\<not> finite S" hence ?thesis by simp}
  moreover
  {assume fS: "finite S"
    have ?thesis
    proof(rule finite_induct[OF fS])
      show "setsum f {} oo a = (\<Sum>i\<in>{}. f i oo a)" by simp
    next
      fix x F assume fF: "finite F" and xF: "x \<notin> F" and h: "setsum f F oo a = setsum (\<lambda>i. f i oo a) F"
      show "setsum f (insert x F) oo a  = setsum (\<lambda>i. f i oo a) (insert x F)"
	using fF xF h by (simp add: fps_compose_add_distrib)
    qed}
  ultimately show ?thesis by blast
qed

lemma convolution_eq:
  "setsum (%i. a (i :: nat) * b (n - i)) {0 .. n} = setsum (%(i,j). a i * b j) {(i,j). i <= n \<and> j \<le> n \<and> i + j = n}"
  apply (rule setsum_reindex_cong[where f=fst])
  apply (clarsimp simp add: inj_on_def)
  apply (auto simp add: expand_set_eq image_iff)
  apply (rule_tac x= "x" in exI)
  apply clarsimp
  apply (rule_tac x="n - x" in exI)
  apply arith
  done

lemma product_composition_lemma:
  assumes c0: "c$0 = (0::'a::idom)" and d0: "d$0 = 0"
  shows "((a oo c) * (b oo d))$n = setsum (%(k,m). a$k * b$m * (c^k * d^m) $ n) {(k,m). k + m \<le> n}" (is "?l = ?r")
proof-
  let ?S = "{(k\<Colon>nat, m\<Colon>nat). k + m \<le> n}"
  have s: "?S \<subseteq> {0..n} <*> {0..n}" by (auto simp add: subset_eq)
  have f: "finite {(k\<Colon>nat, m\<Colon>nat). k + m \<le> n}"
    apply (rule finite_subset[OF s])
    by auto
  have "?r =  setsum (%i. setsum (%(k,m). a$k * (c^k)$i * b$m * (d^m) $ (n - i)) {(k,m). k + m \<le> n}) {0..n}"
    apply (simp add: fps_mult_nth setsum_right_distrib)
    apply (subst setsum_commute)
    apply (rule setsum_cong2)
    by (auto simp add: ring_simps)
  also have "\<dots> = ?l"
    apply (simp add: fps_mult_nth fps_compose_nth setsum_product)
    apply (rule setsum_cong2)
    apply (simp add: setsum_cartesian_product mult_assoc)
    apply (rule setsum_mono_zero_right[OF f])
    apply (simp add: subset_eq) apply presburger
    apply clarsimp
    apply (rule ccontr)
    apply (clarsimp simp add: not_le)
    apply (case_tac "x < aa")
    apply simp
    apply (frule_tac startsby_zero_power_prefix[rule_format, OF c0])
    apply blast
    apply simp
    apply (frule_tac startsby_zero_power_prefix[rule_format, OF d0])
    apply blast
    done
  finally show ?thesis by simp
qed

lemma product_composition_lemma':
  assumes c0: "c$0 = (0::'a::idom)" and d0: "d$0 = 0"
  shows "((a oo c) * (b oo d))$n = setsum (%k. setsum (%m. a$k * b$m * (c^k * d^m) $ n) {0..n}) {0..n}" (is "?l = ?r")
  unfolding product_composition_lemma[OF c0 d0]
  unfolding setsum_cartesian_product
  apply (rule setsum_mono_zero_left)
  apply simp
  apply (clarsimp simp add: subset_eq)
  apply clarsimp
  apply (rule ccontr)
  apply (subgoal_tac "(c^aa * d^ba) $ n = 0")
  apply simp
  unfolding fps_mult_nth
  apply (rule setsum_0')
  apply (clarsimp simp add: not_le)
  apply (case_tac "aaa < aa")
  apply (rule startsby_zero_power_prefix[OF c0, rule_format])
  apply simp
  apply (subgoal_tac "n - aaa < ba")
  apply (frule_tac k = "ba" in startsby_zero_power_prefix[OF d0, rule_format])
  apply simp
  apply arith
  done


lemma setsum_pair_less_iff:
  "setsum (%((k::nat),m). a k * b m * c (k + m)) {(k,m). k + m \<le> n} = setsum (%s. setsum (%i. a i * b (s - i) * c s) {0..s}) {0..n}" (is "?l = ?r")
proof-
  let ?KM=  "{(k,m). k + m \<le> n}"
  let ?f = "%s. UNION {(0::nat)..s} (%i. {(i,s - i)})"
  have th0: "?KM = UNION {0..n} ?f"
    apply (simp add: expand_set_eq)
    apply arith (* FIXME: VERY slow! *)
    done
  show "?l = ?r "
    unfolding th0
    apply (subst setsum_UN_disjoint)
    apply auto
    apply (subst setsum_UN_disjoint)
    apply auto
    done
qed

lemma fps_compose_mult_distrib_lemma:
  assumes c0: "c$0 = (0::'a::idom)"
  shows "((a oo c) * (b oo c))$n = setsum (%s. setsum (%i. a$i * b$(s - i) * (c^s) $ n) {0..s}) {0..n}" (is "?l = ?r")
  unfolding product_composition_lemma[OF c0 c0] power_add[symmetric]
  unfolding setsum_pair_less_iff[where a = "%k. a$k" and b="%m. b$m" and c="%s. (c ^ s)$n" and n = n] ..


lemma fps_compose_mult_distrib:
  assumes c0: "c$0 = (0::'a::idom)"
  shows "(a * b) oo c = (a oo c) * (b oo c)" (is "?l = ?r")
  apply (simp add: fps_eq_iff fps_compose_mult_distrib_lemma[OF c0])
  by (simp add: fps_compose_nth fps_mult_nth setsum_left_distrib)
lemma fps_compose_setprod_distrib:
  assumes c0: "c$0 = (0::'a::idom)"
  shows "(setprod a S) oo c = setprod (%k. a k oo c) S" (is "?l = ?r")
  apply (cases "finite S")
  apply simp_all
  apply (induct S rule: finite_induct)
  apply simp
  apply (simp add: fps_compose_mult_distrib[OF c0])
  done

lemma fps_compose_power:   assumes c0: "c$0 = (0::'a::idom)"
  shows "(a oo c)^n = a^n oo c" (is "?l = ?r")
proof-
  {assume "n=0" then have ?thesis by simp}
  moreover
  {fix m assume m: "n = Suc m"
    have th0: "a^n = setprod (%k. a) {0..m}" "(a oo c) ^ n = setprod (%k. a oo c) {0..m}"
      by (simp_all add: setprod_constant m)
    then have ?thesis
      by (simp add: fps_compose_setprod_distrib[OF c0])}
  ultimately show ?thesis by (cases n, auto)
qed

lemma fps_const_mult_apply_left:
  "fps_const c * (a oo b) = (fps_const c * a) oo b"
  by (simp add: fps_eq_iff fps_compose_nth setsum_right_distrib mult_assoc)

lemma fps_const_mult_apply_right:
  "(a oo b) * fps_const (c::'a::comm_semiring_1) = (fps_const c * a) oo b"
  by (auto simp add: fps_const_mult_apply_left mult_commute)

lemma fps_compose_assoc:
  assumes c0: "c$0 = (0::'a::idom)" and b0: "b$0 = 0"
  shows "a oo (b oo c) = a oo b oo c" (is "?l = ?r")
proof-
  {fix n
    have "?l$n = (setsum (\<lambda>i. (fps_const (a$i) * b^i) oo c) {0..n})$n"
      by (simp add: fps_compose_nth fps_compose_power[OF c0] fps_const_mult_apply_left setsum_right_distrib mult_assoc fps_setsum_nth)
    also have "\<dots> = ((setsum (\<lambda>i. fps_const (a$i) * b^i) {0..n}) oo c)$n"
      by (simp add: fps_compose_setsum_distrib)
    also have "\<dots> = ?r$n"
      apply (simp add: fps_compose_nth fps_setsum_nth setsum_left_distrib mult_assoc)
      apply (rule setsum_cong2)
      apply (rule setsum_mono_zero_right)
      apply (auto simp add: not_le)
      by (erule startsby_zero_power_prefix[OF b0, rule_format])
    finally have "?l$n = ?r$n" .}
  then show ?thesis by (simp add: fps_eq_iff)
qed


lemma fps_X_power_compose:
  assumes a0: "a$0=0" shows "X^k oo a = (a::('a::idom fps))^k" (is "?l = ?r")
proof-
  {assume "k=0" hence ?thesis by simp}
  moreover
  {fix h assume h: "k = Suc h"
    {fix n
      {assume kn: "k>n" hence "?l $ n = ?r $n" using a0 startsby_zero_power_prefix[OF a0] h
	  by (simp add: fps_compose_nth del: power_Suc)}
      moreover
      {assume kn: "k \<le> n"
	hence "?l$n = ?r$n"
          by (simp add: fps_compose_nth mult_delta_left setsum_delta)}
      moreover have "k >n \<or> k\<le> n"  by arith
      ultimately have "?l$n = ?r$n"  by blast}
    then have ?thesis unfolding fps_eq_iff by blast}
  ultimately show ?thesis by (cases k, auto)
qed

lemma fps_inv_right: assumes a0: "a$0 = 0" and a1: "a$1 \<noteq> 0"
  shows "a oo fps_inv a = X"
proof-
  let ?ia = "fps_inv a"
  let ?iaa = "a oo fps_inv a"
  have th0: "?ia $ 0 = 0" by (simp add: fps_inv_def)
  have th1: "?iaa $ 0 = 0" using a0 a1
    by (simp add: fps_inv_def fps_compose_nth)
  have th2: "X$0 = 0" by simp
  from fps_inv[OF a0 a1] have "a oo (fps_inv a oo a) = a oo X" by simp
  then have "(a oo fps_inv a) oo a = X oo a"
    by (simp add: fps_compose_assoc[OF a0 th0] X_fps_compose_startby0[OF a0])
  with fps_compose_inj_right[OF a0 a1]
  show ?thesis by simp
qed

lemma fps_inv_deriv:
  assumes a0:"a$0 = (0::'a::{field})" and a1: "a$1 \<noteq> 0"
  shows "fps_deriv (fps_inv a) = inverse (fps_deriv a oo fps_inv a)"
proof-
  let ?ia = "fps_inv a"
  let ?d = "fps_deriv a oo ?ia"
  let ?dia = "fps_deriv ?ia"
  have ia0: "?ia$0 = 0" by (simp add: fps_inv_def)
  have th0: "?d$0 \<noteq> 0" using a1 by (simp add: fps_compose_nth fps_deriv_nth)
  from fps_inv_right[OF a0 a1] have "?d * ?dia = 1"
    by (simp add: fps_compose_deriv[OF ia0, of a, symmetric] )
  hence "inverse ?d * ?d * ?dia = inverse ?d * 1" by simp
  with inverse_mult_eq_1[OF th0]
  show "?dia = inverse ?d" by simp
qed

subsection{* Elementary series *}

subsubsection{* Exponential series *}
definition "E x = Abs_fps (\<lambda>n. x^n / of_nat (fact n))"

lemma E_deriv[simp]: "fps_deriv (E a) = fps_const (a::'a::{field, ring_char_0}) * E a" (is "?l = ?r")
proof-
  {fix n
    have "?l$n = ?r $ n"
  apply (auto simp add: E_def field_simps power_Suc[symmetric]simp del: fact_Suc of_nat_Suc power_Suc)
  by (simp add: of_nat_mult ring_simps)}
then show ?thesis by (simp add: fps_eq_iff)
qed

lemma E_unique_ODE:
  "fps_deriv a = fps_const c * a \<longleftrightarrow> a = fps_const (a$0) * E (c :: 'a::{field, ring_char_0})"
  (is "?lhs \<longleftrightarrow> ?rhs")
proof-
  {assume d: ?lhs
  from d have th: "\<And>n. a $ Suc n = c * a$n / of_nat (Suc n)"
    by (simp add: fps_deriv_def fps_eq_iff field_simps del: of_nat_Suc)
  {fix n have "a$n = a$0 * c ^ n/ (of_nat (fact n))"
      apply (induct n)
      apply simp
      unfolding th
      using fact_gt_zero
      apply (simp add: field_simps del: of_nat_Suc fact.simps)
      apply (drule sym)
      by (simp add: ring_simps of_nat_mult power_Suc)}
  note th' = this
  have ?rhs
    by (auto simp add: fps_eq_iff fps_const_mult_left E_def intro : th')}
moreover
{assume h: ?rhs
  have ?lhs
    apply (subst h)
    apply simp
    apply (simp only: h[symmetric])
  by simp}
ultimately show ?thesis by blast
qed

lemma E_add_mult: "E (a + b) = E (a::'a::{ring_char_0, field}) * E b" (is "?l = ?r")
proof-
  have "fps_deriv (?r) = fps_const (a+b) * ?r"
    by (simp add: fps_const_add[symmetric] ring_simps del: fps_const_add)
  then have "?r = ?l" apply (simp only: E_unique_ODE)
    by (simp add: fps_mult_nth E_def)
  then show ?thesis ..
qed

lemma E_nth[simp]: "E a $ n = a^n / of_nat (fact n)"
  by (simp add: E_def)

lemma E0[simp]: "E (0::'a::{field}) = 1"
  by (simp add: fps_eq_iff power_0_left)

lemma E_neg: "E (- a) = inverse (E (a::'a::{ring_char_0, field}))"
proof-
  from E_add_mult[of a "- a"] have th0: "E a * E (- a) = 1"
    by (simp )
  have th1: "E a $ 0 \<noteq> 0" by simp
  from fps_inverse_unique[OF th1 th0] show ?thesis by simp
qed

lemma E_nth_deriv[simp]: "fps_nth_deriv n (E (a::'a::{field, ring_char_0})) = (fps_const a)^n * (E a)"
  by (induct n, auto simp add: power_Suc)

lemma fps_compose_uminus: "- (a::'a::ring_1 fps) oo c = - (a oo c)"
  by (simp add: fps_eq_iff fps_compose_nth ring_simps setsum_negf[symmetric])

lemma fps_compose_sub_distrib:
  shows "(a - b) oo (c::'a::ring_1 fps) = (a oo c) - (b oo c)"
  unfolding diff_minus fps_compose_uminus fps_compose_add_distrib ..

lemma X_fps_compose:"X oo a = Abs_fps (\<lambda>n. if n = 0 then (0::'a::comm_ring_1) else a$n)"
  by (simp add: fps_eq_iff fps_compose_nth mult_delta_left setsum_delta power_Suc)

lemma X_compose_E[simp]: "X oo E (a::'a::{field}) = E a - 1"
  by (simp add: fps_eq_iff X_fps_compose)

lemma LE_compose:
  assumes a: "a\<noteq>0"
  shows "fps_inv (E a - 1) oo (E a - 1) = X"
  and "(E a - 1) oo fps_inv (E a - 1) = X"
proof-
  let ?b = "E a - 1"
  have b0: "?b $ 0 = 0" by simp
  have b1: "?b $ 1 \<noteq> 0" by (simp add: a)
  from fps_inv[OF b0 b1] show "fps_inv (E a - 1) oo (E a - 1) = X" .
  from fps_inv_right[OF b0 b1] show "(E a - 1) oo fps_inv (E a - 1) = X" .
qed


lemma fps_const_inverse:
  "inverse (fps_const (a::'a::{field, division_by_zero})) = fps_const (inverse a)"
  apply (auto simp add: fps_eq_iff fps_inverse_def) by (case_tac "n", auto)


lemma inverse_one_plus_X:
  "inverse (1 + X) = Abs_fps (\<lambda>n. (- 1 ::'a::{field})^n)"
  (is "inverse ?l = ?r")
proof-
  have th: "?l * ?r = 1"
    apply (auto simp add: ring_simps fps_eq_iff X_mult_nth  minus_one_power_iff)
    apply presburger+
    done
  have th': "?l $ 0 \<noteq> 0" by (simp add: )
  from fps_inverse_unique[OF th' th] show ?thesis .
qed

lemma E_power_mult: "(E (c::'a::{field,ring_char_0}))^n = E (of_nat n * c)"
  by (induct n, auto simp add: ring_simps E_add_mult power_Suc)

subsubsection{* Logarithmic series *}
definition "(L::'a::{field, ring_char_0} fps)
  = Abs_fps (\<lambda>n. (- 1) ^ Suc n / of_nat n)"

lemma fps_deriv_L: "fps_deriv L = inverse (1 + X)"
  unfolding inverse_one_plus_X
  by (simp add: L_def fps_eq_iff power_Suc del: of_nat_Suc)

lemma L_nth: "L $ n = (- 1) ^ Suc n / of_nat n"
  by (simp add: L_def)

lemma L_E_inv:
  assumes a: "a\<noteq> (0::'a::{field,division_by_zero,ring_char_0})"
  shows "L = fps_const a * fps_inv (E a - 1)" (is "?l = ?r")
proof-
  let ?b = "E a - 1"
  have b0: "?b $ 0 = 0" by simp
  have b1: "?b $ 1 \<noteq> 0" by (simp add: a)
  have "fps_deriv (E a - 1) oo fps_inv (E a - 1) = (fps_const a * (E a - 1) + fps_const a) oo fps_inv (E a - 1)"
    by (simp add: ring_simps)
  also have "\<dots> = fps_const a * (X + 1)" apply (simp add: fps_compose_add_distrib fps_const_mult_apply_left[symmetric] fps_inv_right[OF b0 b1])
    by (simp add: ring_simps)
  finally have eq: "fps_deriv (E a - 1) oo fps_inv (E a - 1) = fps_const a * (X + 1)" .
  from fps_inv_deriv[OF b0 b1, unfolded eq]
  have "fps_deriv (fps_inv ?b) = fps_const (inverse a) / (X + 1)"
    by (simp add: fps_const_inverse eq fps_divide_def fps_inverse_mult)
  hence "fps_deriv (fps_const a * fps_inv ?b) = inverse (X + 1)"
    using a by (simp add: fps_divide_def field_simps)
  hence "fps_deriv ?l = fps_deriv ?r"
    by (simp add: fps_deriv_L add_commute)
  then show ?thesis unfolding fps_deriv_eq_iff
    by (simp add: L_nth fps_inv_def)
qed

subsubsection{* Formal trigonometric functions  *}

definition "fps_sin (c::'a::{field, ring_char_0}) =
  Abs_fps (\<lambda>n. if even n then 0 else (- 1) ^((n - 1) div 2) * c^n /(of_nat (fact n)))"

definition "fps_cos (c::'a::{field, ring_char_0}) = Abs_fps (\<lambda>n. if even n then (- 1) ^ (n div 2) * c^n / (of_nat (fact n)) else 0)"

lemma fps_sin_deriv:
  "fps_deriv (fps_sin c) = fps_const c * fps_cos c"
  (is "?lhs = ?rhs")
proof-
  {fix n::nat
    {assume en: "even n"
      have "?lhs$n = of_nat (n+1) * (fps_sin c $ (n+1))" by simp
      also have "\<dots> = of_nat (n+1) * ((- 1)^(n div 2) * c^Suc n / of_nat (fact (Suc n)))"
	using en by (simp add: fps_sin_def)
      also have "\<dots> = (- 1)^(n div 2) * c^Suc n * (of_nat (n+1) / (of_nat (Suc n) * of_nat (fact n)))"
	unfolding fact_Suc of_nat_mult
	by (simp add: field_simps del: of_nat_add of_nat_Suc)
      also have "\<dots> = (- 1)^(n div 2) *c^Suc n / of_nat (fact n)"
	by (simp add: field_simps del: of_nat_add of_nat_Suc)
      finally have "?lhs $n = ?rhs$n" using en
	by (simp add: fps_cos_def ring_simps power_Suc )}
    then have "?lhs $ n = ?rhs $ n"
      by (cases "even n", simp_all add: fps_deriv_def fps_sin_def fps_cos_def) }
  then show ?thesis by (auto simp add: fps_eq_iff)
qed

lemma fps_cos_deriv:
  "fps_deriv (fps_cos c) = fps_const (- c)* (fps_sin c)"
  (is "?lhs = ?rhs")
proof-
  have th0: "\<And>n. - ((- 1::'a) ^ n) = (- 1)^Suc n" by (simp add: power_Suc)
  have th1: "\<And>n. odd n\<Longrightarrow> Suc ((n - 1) div 2) = Suc n div 2" by presburger (* FIXME: VERY slow! *)
  {fix n::nat
    {assume en: "odd n"
      from en have n0: "n \<noteq>0 " by presburger
      have "?lhs$n = of_nat (n+1) * (fps_cos c $ (n+1))" by simp
      also have "\<dots> = of_nat (n+1) * ((- 1)^((n + 1) div 2) * c^Suc n / of_nat (fact (Suc n)))"
	using en by (simp add: fps_cos_def)
      also have "\<dots> = (- 1)^((n + 1) div 2)*c^Suc n * (of_nat (n+1) / (of_nat (Suc n) * of_nat (fact n)))"
	unfolding fact_Suc of_nat_mult
	by (simp add: field_simps del: of_nat_add of_nat_Suc)
      also have "\<dots> = (- 1)^((n + 1) div 2) * c^Suc n / of_nat (fact n)"
	by (simp add: field_simps del: of_nat_add of_nat_Suc)
      also have "\<dots> = (- ((- 1)^((n - 1) div 2))) * c^Suc n / of_nat (fact n)"
	unfolding th0 unfolding th1[OF en] by simp
      finally have "?lhs $n = ?rhs$n" using en
	by (simp add: fps_sin_def ring_simps power_Suc)}
    then have "?lhs $ n = ?rhs $ n"
      by (cases "even n", simp_all add: fps_deriv_def fps_sin_def
	fps_cos_def) }
  then show ?thesis by (auto simp add: fps_eq_iff)
qed

lemma fps_sin_cos_sum_of_squares:
  "fps_cos c ^ 2 + fps_sin c ^ 2 = 1" (is "?lhs = 1")
proof-
  have "fps_deriv ?lhs = 0"
    apply (simp add:  fps_deriv_power fps_sin_deriv fps_cos_deriv power_Suc)
    by (simp add: ring_simps fps_const_neg[symmetric] del: fps_const_neg)
  then have "?lhs = fps_const (?lhs $ 0)"
    unfolding fps_deriv_eq_0_iff .
  also have "\<dots> = 1"
    by (auto simp add: fps_eq_iff numeral_2_eq_2 fps_mult_nth fps_cos_def fps_sin_def)
  finally show ?thesis .
qed

definition "fps_tan c = fps_sin c / fps_cos c"

lemma fps_tan_deriv: "fps_deriv(fps_tan c) = fps_const c/ (fps_cos c ^ 2)"
proof-
  have th0: "fps_cos c $ 0 \<noteq> 0" by (simp add: fps_cos_def)
  show ?thesis
    using fps_sin_cos_sum_of_squares[of c]
    apply (simp add: fps_tan_def fps_divide_deriv[OF th0] fps_sin_deriv fps_cos_deriv add: fps_const_neg[symmetric] ring_simps power2_eq_square del: fps_const_neg)
    unfolding right_distrib[symmetric]
    by simp
qed

end