src/HOL/ex/ReflectionEx.thy

merged fork with new numeral representation (see NEWS)

(*  Title:      HOL/ex/ReflectionEx.thy
    Author:     Amine Chaieb, TU Muenchen
*)

header {* Examples for generic reflection and reification *}

theory ReflectionEx
imports "~~/src/HOL/Library/Reflection"
begin

text{* This theory presents two methods: reify and reflection *}

text{* 
Consider an HOL type 'a, the structure of which is not recongnisable on the theory level. This is the case of bool, arithmetical terms such as int, real etc \dots
In order to implement a simplification on terms of type 'a we often need its structure.
Traditionnaly such simplifications are written in ML, proofs are synthesized.
An other strategy is to declare an HOL-datatype tau and an HOL function (the interpretation) that maps elements of tau to elements of 'a. The functionality of @{text reify} is to compute a term s::tau, which is the representant of t. For this it needs equations for the interpretation.

NB: All the interpretations supported by @{text reify} must have the type @{text "'b list \<Rightarrow> tau \<Rightarrow> 'a"}.
The method @{text reify} can also be told which subterm of the current subgoal should be reified. The general call for @{text reify} is: @{text "reify eqs (t)"}, where @{text eqs} are the defining equations of the interpretation and @{text "(t)"} is an optional parameter which specifies the subterm to which reification should be applied to. If @{text "(t)"} is abscent, @{text reify} tries to reify the whole subgoal.

The method reflection uses @{text reify} and has a very similar signature: @{text "reflection corr_thm eqs (t)"}. Here again @{text eqs} and @{text "(t)"} are as described above and @{text corr_thm} is a thorem proving @{term "I vs (f t) = I vs t"}. We assume that @{text I} is the interpretation and @{text f} is some useful and executable simplification of type @{text "tau \<Rightarrow> tau"}. The method @{text reflection} applies reification and hence the theorem @{term "t = I xs s"} and hence using @{text corr_thm} derives @{term "t = I xs (f s)"}. It then uses normalization by evaluation to prove @{term "f s = s'"} which almost finishes the proof of @{term "t = t'"} where @{term "I xs s' = t'"}.
*}

text{* Example 1 : Propositional formulae and NNF.*}
text{* The type @{text fm} represents simple propositional formulae: *}

datatype form = TrueF | FalseF | Less nat nat |
                And form form | Or form form | Neg form | ExQ form

fun interp :: "form \<Rightarrow> ('a::ord) list \<Rightarrow> bool" where
"interp TrueF e = True" |
"interp FalseF e = False" |
"interp (Less i j) e = (e!i < e!j)" |
"interp (And f1 f2) e = (interp f1 e & interp f2 e)" |
"interp (Or f1 f2) e = (interp f1 e | interp f2 e)" |
"interp (Neg f) e = (~ interp f e)" |
"interp (ExQ f) e = (EX x. interp f (x#e))"

lemmas interp_reify_eqs = interp.simps
declare interp_reify_eqs[reify]

lemma "EX x. x < y & x < z"
  apply (reify )
  oops

datatype fm = And fm fm | Or fm fm | Imp fm fm | Iff fm fm | NOT fm | At nat

primrec Ifm :: "fm \<Rightarrow> bool list \<Rightarrow> bool" where
  "Ifm (At n) vs = vs!n"
| "Ifm (And p q) vs = (Ifm p vs \<and> Ifm q vs)"
| "Ifm (Or p q) vs = (Ifm p vs \<or> Ifm q vs)"
| "Ifm (Imp p q) vs = (Ifm p vs \<longrightarrow> Ifm q vs)"
| "Ifm (Iff p q) vs = (Ifm p vs = Ifm q vs)"
| "Ifm (NOT p) vs = (\<not> (Ifm p vs))"

lemma "Q \<longrightarrow> (D & F & ((~ D) & (~ F)))"
apply (reify Ifm.simps)
oops

  text{* Method @{text reify} maps a bool to an fm. For this it needs the 
  semantics of fm, i.e.\ the rewrite rules in @{text Ifm.simps}. *}


  (* You can also just pick up a subterm to reify \<dots> *)
lemma "Q \<longrightarrow> (D & F & ((~ D) & (~ F)))"
apply (reify Ifm.simps ("((~ D) & (~ F))"))
oops

  text{* Let's perform NNF. This is a version that tends to generate disjunctions *}
primrec fmsize :: "fm \<Rightarrow> nat" where
  "fmsize (At n) = 1"
| "fmsize (NOT p) = 1 + fmsize p"
| "fmsize (And p q) = 1 + fmsize p + fmsize q"
| "fmsize (Or p q) = 1 + fmsize p + fmsize q"
| "fmsize (Imp p q) = 2 + fmsize p + fmsize q"
| "fmsize (Iff p q) = 2 + 2* fmsize p + 2* fmsize q"

lemma [measure_function]: "is_measure fmsize" ..

fun nnf :: "fm \<Rightarrow> fm"
where
  "nnf (At n) = At n"
| "nnf (And p q) = And (nnf p) (nnf q)"
| "nnf (Or p q) = Or (nnf p) (nnf q)"
| "nnf (Imp p q) = Or (nnf (NOT p)) (nnf q)"
| "nnf (Iff p q) = Or (And (nnf p) (nnf q)) (And (nnf (NOT p)) (nnf (NOT q)))"
| "nnf (NOT (And p q)) = Or (nnf (NOT p)) (nnf (NOT q))"
| "nnf (NOT (Or p q)) = And (nnf (NOT p)) (nnf (NOT q))"
| "nnf (NOT (Imp p q)) = And (nnf p) (nnf (NOT q))"
| "nnf (NOT (Iff p q)) = Or (And (nnf p) (nnf (NOT q))) (And (nnf (NOT p)) (nnf q))"
| "nnf (NOT (NOT p)) = nnf p"
| "nnf (NOT p) = NOT p"

  text{* The correctness theorem of nnf: it preserves the semantics of fm *}
lemma nnf[reflection]: "Ifm (nnf p) vs = Ifm p vs"
  by (induct p rule: nnf.induct) auto

  text{* Now let's perform NNF using our @{term nnf} function defined above. First to the whole subgoal. *}
lemma "(\<not> (A = B)) \<and> (B \<longrightarrow> (A \<noteq> (B | C \<and> (B \<longrightarrow> A | D)))) \<longrightarrow> A \<or> B \<and> D"
apply (reflection Ifm.simps)
oops

  text{* Now we specify on which subterm it should be applied*}
lemma "(\<not> (A = B)) \<and> (B \<longrightarrow> (A \<noteq> (B | C \<and> (B \<longrightarrow> A | D)))) \<longrightarrow> A \<or> B \<and> D"
apply (reflection Ifm.simps only: "(B | C \<and> (B \<longrightarrow> A | D))")
oops


  (* Example 2 : Simple arithmetic formulae *)

  text{* The type @{text num} reflects linear expressions over natural number *}
datatype num = C nat | Add num num | Mul nat num | Var nat | CN nat nat num

text{* This is just technical to make recursive definitions easier. *}
primrec num_size :: "num \<Rightarrow> nat" 
where
  "num_size (C c) = 1"
| "num_size (Var n) = 1"
| "num_size (Add a b) = 1 + num_size a + num_size b"
| "num_size (Mul c a) = 1 + num_size a"
| "num_size (CN n c a) = 4 + num_size a "

  text{* The semantics of num *}
primrec Inum:: "num \<Rightarrow> nat list \<Rightarrow> nat"
where
  Inum_C  : "Inum (C i) vs = i"
| Inum_Var: "Inum (Var n) vs = vs!n"
| Inum_Add: "Inum (Add s t) vs = Inum s vs + Inum t vs "
| Inum_Mul: "Inum (Mul c t) vs = c * Inum t vs "
| Inum_CN : "Inum (CN n c t) vs = c*(vs!n) + Inum t vs "


  text{* Let's reify some nat expressions \dots *}
lemma "4 * (2*x + (y::nat)) + f a \<noteq> 0"
  apply (reify Inum.simps ("4 * (2*x + (y::nat)) + f a"))
oops
text{* We're in a bad situation!! x, y and f a have been recongnized as a constants, which is correct but does not correspond to our intuition of the constructor C. It should encapsulate constants, i.e. numbers, i.e. numerals.*}

  text{* So let's leave the @{text "Inum_C"} equation at the end and see what happens \dots*}
lemma "4 * (2*x + (y::nat)) \<noteq> 0"
  apply (reify Inum_Var Inum_Add Inum_Mul Inum_CN Inum_C ("4 * (2*x + (y::nat))"))
oops
text{* Hmmm let's specialize @{text Inum_C} with numerals.*}

lemma Inum_number: "Inum (C (numeral t)) vs = numeral t" by simp
lemmas Inum_eqs = Inum_Var Inum_Add Inum_Mul Inum_CN Inum_number

  text{* Second attempt *}
lemma "1 * (2*x + (y::nat)) \<noteq> 0"
  apply (reify Inum_eqs ("1 * (2*x + (y::nat))"))
oops
  text{* That was fine, so let's try another one \dots *}

lemma "1 * (2* x + (y::nat) + 0 + 1) \<noteq> 0"
  apply (reify Inum_eqs ("1 * (2*x + (y::nat) + 0 + 1)"))
oops
  text{* Oh!! 0 is not a variable \dots\ Oh! 0 is not a @{text "numeral"} \dots\ thing. The same for 1. So let's add those equations too *}

lemma Inum_01: "Inum (C 0) vs = 0" "Inum (C 1) vs = 1" "Inum (C(Suc n)) vs = Suc n"
  by simp+

lemmas Inum_eqs'= Inum_eqs Inum_01

text{* Third attempt: *}

lemma "1 * (2*x + (y::nat) + 0 + 1) \<noteq> 0"
  apply (reify Inum_eqs' ("1 * (2*x + (y::nat) + 0 + 1)"))
oops
text{* Okay, let's try reflection. Some simplifications on num follow. You can skim until the main theorem @{text linum} *}
fun lin_add :: "num \<Rightarrow> num \<Rightarrow> num"
where
  "lin_add (CN n1 c1 r1) (CN n2 c2 r2) =
  (if n1=n2 then 
  (let c = c1 + c2
  in (if c=0 then lin_add r1 r2 else CN n1 c (lin_add r1 r2)))
  else if n1 \<le> n2 then (CN n1 c1 (lin_add r1 (CN n2 c2 r2))) 
  else (CN n2 c2 (lin_add (CN n1 c1 r1) r2)))"
| "lin_add (CN n1 c1 r1) t = CN n1 c1 (lin_add r1 t)"  
| "lin_add t (CN n2 c2 r2) = CN n2 c2 (lin_add t r2)" 
| "lin_add (C b1) (C b2) = C (b1+b2)"
| "lin_add a b = Add a b"
lemma lin_add: "Inum (lin_add t s) bs = Inum (Add t s) bs"
apply (induct t s rule: lin_add.induct, simp_all add: Let_def)
apply (case_tac "c1+c2 = 0",case_tac "n1 \<le> n2", simp_all)
by (case_tac "n1 = n2", simp_all add: algebra_simps)

fun lin_mul :: "num \<Rightarrow> nat \<Rightarrow> num"
where
  "lin_mul (C j) i = C (i*j)"
| "lin_mul (CN n c a) i = (if i=0 then (C 0) else CN n (i*c) (lin_mul a i))"
| "lin_mul t i = (Mul i t)"

lemma lin_mul: "Inum (lin_mul t i) bs = Inum (Mul i t) bs"
by (induct t i rule: lin_mul.induct, auto simp add: algebra_simps)

lemma [measure_function]: "is_measure num_size" ..

fun linum:: "num \<Rightarrow> num"
where
  "linum (C b) = C b"
| "linum (Var n) = CN n 1 (C 0)"
| "linum (Add t s) = lin_add (linum t) (linum s)"
| "linum (Mul c t) = lin_mul (linum t) c"
| "linum (CN n c t) = lin_add (linum (Mul c (Var n))) (linum t)"

lemma linum[reflection] : "Inum (linum t) bs = Inum t bs"
by (induct t rule: linum.induct, simp_all add: lin_mul lin_add)

  text{* Now we can use linum to simplify nat terms using reflection *}
lemma "(Suc (Suc 1)) * (x + (Suc 1)*y) = 3*x + 6*y"
 apply (reflection Inum_eqs' only: "(Suc (Suc 1)) * (x + (Suc 1)*y)") 
oops

  text{* Let's lift this to formulae and see what happens *}

datatype aform = Lt num num  | Eq num num | Ge num num | NEq num num | 
  Conj aform aform | Disj aform aform | NEG aform | T | F

primrec linaformsize:: "aform \<Rightarrow> nat"
where
  "linaformsize T = 1"
| "linaformsize F = 1"
| "linaformsize (Lt a b) = 1"
| "linaformsize (Ge a b) = 1"
| "linaformsize (Eq a b) = 1"
| "linaformsize (NEq a b) = 1"
| "linaformsize (NEG p) = 2 + linaformsize p"
| "linaformsize (Conj p q) = 1 + linaformsize p + linaformsize q"
| "linaformsize (Disj p q) = 1 + linaformsize p + linaformsize q"

lemma [measure_function]: "is_measure linaformsize" ..

primrec is_aform :: "aform => nat list => bool"
where
  "is_aform T vs = True"
| "is_aform F vs = False"
| "is_aform (Lt a b) vs = (Inum a vs < Inum b vs)"
| "is_aform (Eq a b) vs = (Inum a vs = Inum b vs)"
| "is_aform (Ge a b) vs = (Inum a vs \<ge> Inum b vs)"
| "is_aform (NEq a b) vs = (Inum a vs \<noteq> Inum b vs)"
| "is_aform (NEG p) vs = (\<not> (is_aform p vs))"
| "is_aform (Conj p q) vs = (is_aform p vs \<and> is_aform q vs)"
| "is_aform (Disj p q) vs = (is_aform p vs \<or> is_aform q vs)"

  text{* Let's reify and do reflection *}
lemma "(3::nat)*x + t < 0 \<and> (2 * x + y \<noteq> 17)"
 apply (reify Inum_eqs' is_aform.simps) 
oops

text{* Note that reification handles several interpretations at the same time*}
lemma "(3::nat)*x + t < 0 & x*x + t*x + 3 + 1 = z*t*4*z | x + x + 1 < 0"
 apply (reflection Inum_eqs' is_aform.simps only:"x + x + 1") 
oops

  text{* For reflection we now define a simple transformation on aform: NNF + linum on atoms *}

fun linaform:: "aform \<Rightarrow> aform"
where
  "linaform (Lt s t) = Lt (linum s) (linum t)"
| "linaform (Eq s t) = Eq (linum s) (linum t)"
| "linaform (Ge s t) = Ge (linum s) (linum t)"
| "linaform (NEq s t) = NEq (linum s) (linum t)"
| "linaform (Conj p q) = Conj (linaform p) (linaform q)"
| "linaform (Disj p q) = Disj (linaform p) (linaform q)"
| "linaform (NEG T) = F"
| "linaform (NEG F) = T"
| "linaform (NEG (Lt a b)) = Ge a b"
| "linaform (NEG (Ge a b)) = Lt a b"
| "linaform (NEG (Eq a b)) = NEq a b"
| "linaform (NEG (NEq a b)) = Eq a b"
| "linaform (NEG (NEG p)) = linaform p"
| "linaform (NEG (Conj p q)) = Disj (linaform (NEG p)) (linaform (NEG q))"
| "linaform (NEG (Disj p q)) = Conj (linaform (NEG p)) (linaform (NEG q))"
| "linaform p = p"

lemma linaform: "is_aform (linaform p) vs = is_aform p vs"
  by (induct p rule: linaform.induct) (auto simp add: linum)

lemma "(((Suc(Suc (Suc 0)))*((x::nat) + (Suc (Suc 0)))) + (Suc (Suc (Suc 0))) * ((Suc(Suc (Suc 0)))*((x::nat) + (Suc (Suc 0))))< 0) \<and> (Suc 0  + Suc 0< 0)"
   apply (reflection Inum_eqs' is_aform.simps rules: linaform)  
oops

declare linaform[reflection]
lemma "(((Suc(Suc (Suc 0)))*((x::nat) + (Suc (Suc 0)))) + (Suc (Suc (Suc 0))) * ((Suc(Suc (Suc 0)))*((x::nat) + (Suc (Suc 0))))< 0) \<and> (Suc 0  + Suc 0< 0)"
   apply (reflection Inum_eqs' is_aform.simps)
oops

text{* We now give an example where Interpretaions have 0 or more than only one envornement of different types and show that automatic reification also deals with binding *}
datatype rb = BC bool| BAnd rb rb | BOr rb rb
primrec Irb :: "rb \<Rightarrow> bool"
where
  "Irb (BC p) = p"
| "Irb (BAnd s t) = (Irb s \<and> Irb t)"
| "Irb (BOr s t) = (Irb s \<or> Irb t)"

lemma "A \<and> (B \<or> D \<and> B) \<and> A \<and> (B \<or> D \<and> B) \<or> A \<and> (B \<or> D \<and> B) \<or> A \<and> (B \<or> D \<and> B)"
apply (reify Irb.simps)
oops


datatype rint = IC int| IVar nat | IAdd rint rint | IMult rint rint | INeg rint | ISub rint rint
primrec Irint :: "rint \<Rightarrow> int list \<Rightarrow> int"
where
  Irint_Var: "Irint (IVar n) vs = vs!n"
| Irint_Neg: "Irint (INeg t) vs = - Irint t vs"
| Irint_Add: "Irint (IAdd s t) vs = Irint s vs + Irint t vs"
| Irint_Sub: "Irint (ISub s t) vs = Irint s vs - Irint t vs"
| Irint_Mult: "Irint (IMult s t) vs = Irint s vs * Irint t vs"
| Irint_C: "Irint (IC i) vs = i"
lemma Irint_C0: "Irint (IC 0) vs = 0"
  by simp
lemma Irint_C1: "Irint (IC 1) vs = 1"
  by simp
lemma Irint_Cnumeral: "Irint (IC (numeral x)) vs = numeral x"
  by simp
lemmas Irint_simps = Irint_Var Irint_Neg Irint_Add Irint_Sub Irint_Mult Irint_C0 Irint_C1 Irint_Cnumeral
lemma "(3::int) * x + y*y - 9 + (- z) = 0"
  apply (reify Irint_simps ("(3::int) * x + y*y - 9 + (- z)"))
  oops
datatype rlist = LVar nat| LEmpty| LCons rint rlist | LAppend rlist rlist
primrec Irlist :: "rlist \<Rightarrow> int list \<Rightarrow> (int list) list \<Rightarrow> (int list)"
where
  "Irlist (LEmpty) is vs = []"
| "Irlist (LVar n) is vs = vs!n"
| "Irlist (LCons i t) is vs = ((Irint i is)#(Irlist t is vs))"
| "Irlist (LAppend s t) is vs = (Irlist s is vs) @ (Irlist t is vs)"
lemma "[(1::int)] = []"
  apply (reify Irlist.simps Irint_simps ("[1]:: int list"))
  oops

lemma "([(3::int) * x + y*y - 9 + (- z)] @ []) @ xs = [y*y - z - 9 + (3::int) * x]"
  apply (reify Irlist.simps Irint_simps ("([(3::int) * x + y*y - 9 + (- z)] @ []) @ xs"))
  oops

datatype rnat = NC nat| NVar nat| NSuc rnat | NAdd rnat rnat | NMult rnat rnat | NNeg rnat | NSub rnat rnat | Nlgth rlist
primrec Irnat :: "rnat \<Rightarrow> int list \<Rightarrow> (int list) list \<Rightarrow> nat list \<Rightarrow> nat"
where
  Irnat_Suc: "Irnat (NSuc t) is ls vs = Suc (Irnat t is ls vs)"
| Irnat_Var: "Irnat (NVar n) is ls vs = vs!n"
| Irnat_Neg: "Irnat (NNeg t) is ls vs = 0"
| Irnat_Add: "Irnat (NAdd s t) is ls vs = Irnat s is ls vs + Irnat t is ls vs"
| Irnat_Sub: "Irnat (NSub s t) is ls vs = Irnat s is ls vs - Irnat t is ls vs"
| Irnat_Mult: "Irnat (NMult s t) is ls vs = Irnat s is ls vs * Irnat t is ls vs"
| Irnat_lgth: "Irnat (Nlgth rxs) is ls vs = length (Irlist rxs is ls)"
| Irnat_C: "Irnat (NC i) is ls vs = i"
lemma Irnat_C0: "Irnat (NC 0) is ls vs = 0"
by simp
lemma Irnat_C1: "Irnat (NC 1) is ls vs = 1"
by simp
lemma Irnat_Cnumeral: "Irnat (NC (numeral x)) is ls vs = numeral x"
by simp
lemmas Irnat_simps = Irnat_Suc Irnat_Var Irnat_Neg Irnat_Add Irnat_Sub Irnat_Mult Irnat_lgth
  Irnat_C0 Irnat_C1 Irnat_Cnumeral
lemma "(Suc n) * length (([(3::int) * x + y*y - 9 + (- z)] @ []) @ xs) = length xs"
  apply (reify Irnat_simps Irlist.simps Irint_simps ("(Suc n) *length (([(3::int) * x + y*y - 9 + (- z)] @ []) @ xs)"))
  oops
datatype rifm = RT | RF | RVar nat
  | RNLT rnat rnat | RNILT rnat rint | RNEQ rnat rnat
  |RAnd rifm rifm | ROr rifm rifm | RImp rifm rifm| RIff rifm rifm
  | RNEX rifm | RIEX rifm| RLEX rifm | RNALL rifm | RIALL rifm| RLALL rifm
  | RBEX rifm | RBALL rifm

primrec Irifm :: "rifm \<Rightarrow> bool list \<Rightarrow> int list \<Rightarrow> (int list) list \<Rightarrow> nat list \<Rightarrow> bool"
where
  "Irifm RT ps is ls ns = True"
| "Irifm RF ps is ls ns = False"
| "Irifm (RVar n) ps is ls ns = ps!n"
| "Irifm (RNLT s t) ps is ls ns = (Irnat s is ls ns < Irnat t is ls ns)"
| "Irifm (RNILT s t) ps is ls ns = (int (Irnat s is ls ns) < Irint t is)"
| "Irifm (RNEQ s t) ps is ls ns = (Irnat s is ls ns = Irnat t is ls ns)"
| "Irifm (RAnd p q) ps is ls ns = (Irifm p ps is ls ns \<and> Irifm q ps is ls ns)"
| "Irifm (ROr p q) ps is ls ns = (Irifm p ps is ls ns \<or> Irifm q ps is ls ns)"
| "Irifm (RImp p q) ps is ls ns = (Irifm p ps is ls ns \<longrightarrow> Irifm q ps is ls ns)"
| "Irifm (RIff p q) ps is ls ns = (Irifm p ps is ls ns = Irifm q ps is ls ns)"
| "Irifm (RNEX p) ps is ls ns =  (\<exists>x. Irifm p ps is ls (x#ns))"
| "Irifm (RIEX p) ps is ls ns =  (\<exists>x. Irifm p ps (x#is) ls ns)"
| "Irifm (RLEX p) ps is ls ns =  (\<exists>x. Irifm p ps is (x#ls) ns)"
| "Irifm (RBEX p) ps is ls ns =  (\<exists>x. Irifm p (x#ps) is ls ns)"
| "Irifm (RNALL p) ps is ls ns = (\<forall>x. Irifm p ps is ls (x#ns))"
| "Irifm (RIALL p) ps is ls ns = (\<forall>x. Irifm p ps (x#is) ls ns)"
| "Irifm (RLALL p) ps is ls ns = (\<forall>x. Irifm p ps is (x#ls) ns)"
| "Irifm (RBALL p) ps is ls ns = (\<forall>x. Irifm p (x#ps) is ls ns)"

lemma " \<forall>x. \<exists>n. ((Suc n) * length (([(3::int) * x + (f t)*y - 9 + (- z)] @ []) @ xs) = length xs) \<and> m < 5*n - length (xs @ [2,3,4,x*z + 8 - y]) \<longrightarrow> (\<exists>p. \<forall>q. p \<and> q \<longrightarrow> r)"
  apply (reify Irifm.simps Irnat_simps Irlist.simps Irint_simps)
oops


(* An example for equations containing type variables *)
datatype prod = Zero | One | Var nat | Mul prod prod 
  | Pw prod nat | PNM nat nat prod
primrec Iprod :: " prod \<Rightarrow> ('a::{linordered_idom}) list \<Rightarrow>'a" 
where
  "Iprod Zero vs = 0"
| "Iprod One vs = 1"
| "Iprod (Var n) vs = vs!n"
| "Iprod (Mul a b) vs = (Iprod a vs * Iprod b vs)"
| "Iprod (Pw a n) vs = ((Iprod a vs) ^ n)"
| "Iprod (PNM n k t) vs = (vs ! n)^k * Iprod t vs"

datatype sgn = Pos prod | Neg prod | ZeroEq prod | NZeroEq prod | Tr | F 
  | Or sgn sgn | And sgn sgn

primrec Isgn :: " sgn \<Rightarrow> ('a::{linordered_idom}) list \<Rightarrow>bool"
where 
  "Isgn Tr vs = True"
| "Isgn F vs = False"
| "Isgn (ZeroEq t) vs = (Iprod t vs = 0)"
| "Isgn (NZeroEq t) vs = (Iprod t vs \<noteq> 0)"
| "Isgn (Pos t) vs = (Iprod t vs > 0)"
| "Isgn (Neg t) vs = (Iprod t vs < 0)"
| "Isgn (And p q) vs = (Isgn p vs \<and> Isgn q vs)"
| "Isgn (Or p q) vs = (Isgn p vs \<or> Isgn q vs)"

lemmas eqs = Isgn.simps Iprod.simps

lemma "(x::'a::{linordered_idom})^4 * y * z * y^2 * z^23 > 0"
  apply (reify eqs)
  oops

end