theory W
imports "HOL-Nominal.Nominal"
begin
text \<open>Example for strong induction rules avoiding sets of atoms.\<close>
atom_decl tvar var
abbreviation
"difference_list" :: "'a list \<Rightarrow> 'a list \<Rightarrow> 'a list" ("_ - _" [60,60] 60)
where
"xs - ys \<equiv> [x \<leftarrow> xs. x\<notin>set ys]"
lemma difference_eqvt_tvar[eqvt]:
fixes pi::"tvar prm"
and Xs Ys::"tvar list"
shows "pi\<bullet>(Xs - Ys) = (pi\<bullet>Xs) - (pi\<bullet>Ys)"
by (induct Xs) (simp_all add: eqvts)
lemma difference_fresh:
fixes X::"tvar"
and Xs Ys::"tvar list"
assumes a: "X\<in>set Ys"
shows "X\<sharp>(Xs - Ys)"
using a
by (induct Xs) (auto simp add: fresh_list_nil fresh_list_cons fresh_atm)
lemma difference_supset:
fixes xs::"'a list"
and ys::"'a list"
and zs::"'a list"
assumes asm: "set xs \<subseteq> set ys"
shows "xs - ys = []"
using asm
by (induct xs) (auto)
nominal_datatype ty =
TVar "tvar"
| Fun "ty" "ty" ("_\<rightarrow>_" [100,100] 100)
nominal_datatype tyS =
Ty "ty"
| ALL "\<guillemotleft>tvar\<guillemotright>tyS" ("\<forall>[_]._" [100,100] 100)
nominal_datatype trm =
Var "var"
| App "trm" "trm"
| Lam "\<guillemotleft>var\<guillemotright>trm" ("Lam [_]._" [100,100] 100)
| Let "\<guillemotleft>var\<guillemotright>trm" "trm"
abbreviation
LetBe :: "var \<Rightarrow> trm \<Rightarrow> trm \<Rightarrow> trm" ("Let _ be _ in _" [100,100,100] 100)
where
"Let x be t1 in t2 \<equiv> trm.Let x t2 t1"
type_synonym
Ctxt = "(var\<times>tyS) list"
text \<open>free type variables\<close>
consts ftv :: "'a \<Rightarrow> tvar list"
overloading
ftv_prod \<equiv> "ftv :: ('a \<times> 'b) \<Rightarrow> tvar list"
ftv_tvar \<equiv> "ftv :: tvar \<Rightarrow> tvar list"
ftv_var \<equiv> "ftv :: var \<Rightarrow> tvar list"
ftv_list \<equiv> "ftv :: 'a list \<Rightarrow> tvar list"
ftv_ty \<equiv> "ftv :: ty \<Rightarrow> tvar list"
begin
primrec
ftv_prod
where
"ftv_prod (x, y) = (ftv x) @ (ftv y)"
definition
ftv_tvar :: "tvar \<Rightarrow> tvar list"
where
[simp]: "ftv_tvar X \<equiv> [(X::tvar)]"
definition
ftv_var :: "var \<Rightarrow> tvar list"
where
[simp]: "ftv_var x \<equiv> []"
primrec
ftv_list
where
"ftv_list [] = []"
| "ftv_list (x#xs) = (ftv x)@(ftv_list xs)"
nominal_primrec
ftv_ty :: "ty \<Rightarrow> tvar list"
where
"ftv_ty (TVar X) = [X]"
| "ftv_ty (T1 \<rightarrow>T2) = (ftv_ty T1) @ (ftv_ty T2)"
by (rule TrueI)+
end
lemma ftv_ty_eqvt[eqvt]:
fixes pi::"tvar prm"
and T::"ty"
shows "pi\<bullet>(ftv T) = ftv (pi\<bullet>T)"
by (nominal_induct T rule: ty.strong_induct)
(perm_simp add: append_eqvt)+
overloading
ftv_tyS \<equiv> "ftv :: tyS \<Rightarrow> tvar list"
begin
nominal_primrec
ftv_tyS :: "tyS \<Rightarrow> tvar list"
where
"ftv_tyS (Ty T) = ((ftv (T::ty))::tvar list)"
| "ftv_tyS (\<forall>[X].S) = (ftv_tyS S) - [X]"
apply(finite_guess add: ftv_ty_eqvt fs_tvar1)+
apply(rule TrueI)+
apply(rule difference_fresh)
apply(simp)
apply(fresh_guess add: ftv_ty_eqvt fs_tvar1)+
done
end
lemma ftv_tyS_eqvt[eqvt]:
fixes pi::"tvar prm"
and S::"tyS"
shows "pi\<bullet>(ftv S) = ftv (pi\<bullet>S)"
apply(nominal_induct S rule: tyS.strong_induct)
apply(simp add: eqvts)
apply(simp only: ftv_tyS.simps)
apply(simp only: eqvts)
apply(simp add: eqvts)
done
lemma ftv_Ctxt_eqvt[eqvt]:
fixes pi::"tvar prm"
and \<Gamma>::"Ctxt"
shows "pi\<bullet>(ftv \<Gamma>) = ftv (pi\<bullet>\<Gamma>)"
by (induct \<Gamma>) (auto simp add: eqvts)
text \<open>Valid\<close>
inductive
valid :: "Ctxt \<Rightarrow> bool"
where
V_Nil[intro]: "valid []"
| V_Cons[intro]: "\<lbrakk>valid \<Gamma>;x\<sharp>\<Gamma>\<rbrakk>\<Longrightarrow> valid ((x,S)#\<Gamma>)"
equivariance valid
text \<open>General\<close>
primrec gen :: "ty \<Rightarrow> tvar list \<Rightarrow> tyS" where
"gen T [] = Ty T"
| "gen T (X#Xs) = \<forall>[X].(gen T Xs)"
lemma gen_eqvt[eqvt]:
fixes pi::"tvar prm"
shows "pi\<bullet>(gen T Xs) = gen (pi\<bullet>T) (pi\<bullet>Xs)"
by (induct Xs) (simp_all add: eqvts)
abbreviation
close :: "Ctxt \<Rightarrow> ty \<Rightarrow> tyS"
where
"close \<Gamma> T \<equiv> gen T ((ftv T) - (ftv \<Gamma>))"
lemma close_eqvt[eqvt]:
fixes pi::"tvar prm"
shows "pi\<bullet>(close \<Gamma> T) = close (pi\<bullet>\<Gamma>) (pi\<bullet>T)"
by (simp_all only: eqvts)
text \<open>Substitution\<close>
type_synonym Subst = "(tvar\<times>ty) list"
consts
psubst :: "Subst \<Rightarrow> 'a \<Rightarrow> 'a" ("_<_>" [100,60] 120)
abbreviation
subst :: "'a \<Rightarrow> tvar \<Rightarrow> ty \<Rightarrow> 'a" ("_[_::=_]" [100,100,100] 100)
where
"smth[X::=T] \<equiv> ([(X,T)])<smth>"
fun
lookup :: "Subst \<Rightarrow> tvar \<Rightarrow> ty"
where
"lookup [] X = TVar X"
| "lookup ((Y,T)#\<theta>) X = (if X=Y then T else lookup \<theta> X)"
lemma lookup_eqvt[eqvt]:
fixes pi::"tvar prm"
shows "pi\<bullet>(lookup \<theta> X) = lookup (pi\<bullet>\<theta>) (pi\<bullet>X)"
by (induct \<theta>) (auto simp add: eqvts)
lemma lookup_fresh:
fixes X::"tvar"
assumes a: "X\<sharp>\<theta>"
shows "lookup \<theta> X = TVar X"
using a
by (induct \<theta>)
(auto simp add: fresh_list_cons fresh_prod fresh_atm)
overloading
psubst_ty \<equiv> "psubst :: Subst \<Rightarrow> ty \<Rightarrow> ty"
begin
nominal_primrec
psubst_ty
where
"\<theta><TVar X> = lookup \<theta> X"
| "\<theta><T\<^sub>1 \<rightarrow> T\<^sub>2> = (\<theta><T\<^sub>1>) \<rightarrow> (\<theta><T\<^sub>2>)"
by (rule TrueI)+
end
lemma psubst_ty_eqvt[eqvt]:
fixes pi::"tvar prm"
and \<theta>::"Subst"
and T::"ty"
shows "pi\<bullet>(\<theta><T>) = (pi\<bullet>\<theta>)<(pi\<bullet>T)>"
by (induct T rule: ty.induct) (simp_all add: eqvts)
overloading
psubst_tyS \<equiv> "psubst :: Subst \<Rightarrow> tyS \<Rightarrow> tyS"
begin
nominal_primrec
psubst_tyS :: "Subst \<Rightarrow> tyS \<Rightarrow> tyS"
where
"\<theta><(Ty T)> = Ty (\<theta><T>)"
| "X\<sharp>\<theta> \<Longrightarrow> \<theta><(\<forall>[X].S)> = \<forall>[X].(\<theta><S>)"
apply(finite_guess add: psubst_ty_eqvt fs_tvar1)+
apply(rule TrueI)+
apply(simp add: abs_fresh)
apply(fresh_guess add: psubst_ty_eqvt fs_tvar1)+
done
end
overloading
psubst_Ctxt \<equiv> "psubst :: Subst \<Rightarrow> Ctxt \<Rightarrow> Ctxt"
begin
fun
psubst_Ctxt :: "Subst \<Rightarrow> Ctxt \<Rightarrow> Ctxt"
where
"psubst_Ctxt \<theta> [] = []"
| "psubst_Ctxt \<theta> ((x,S)#\<Gamma>) = (x,\<theta><S>)#(psubst_Ctxt \<theta> \<Gamma>)"
end
lemma fresh_lookup:
fixes X::"tvar"
and \<theta>::"Subst"
and Y::"tvar"
assumes asms: "X\<sharp>Y" "X\<sharp>\<theta>"
shows "X\<sharp>(lookup \<theta> Y)"
using asms
by (induct \<theta>)
(auto simp add: fresh_list_cons fresh_prod fresh_atm)
lemma fresh_psubst_ty:
fixes X::"tvar"
and \<theta>::"Subst"
and T::"ty"
assumes asms: "X\<sharp>\<theta>" "X\<sharp>T"
shows "X\<sharp>\<theta><T>"
using asms
by (nominal_induct T rule: ty.strong_induct)
(auto simp add: fresh_list_append fresh_list_cons fresh_prod fresh_lookup)
lemma fresh_psubst_tyS:
fixes X::"tvar"
and \<theta>::"Subst"
and S::"tyS"
assumes asms: "X\<sharp>\<theta>" "X\<sharp>S"
shows "X\<sharp>\<theta><S>"
using asms
by (nominal_induct S avoiding: \<theta> X rule: tyS.strong_induct)
(auto simp add: fresh_psubst_ty abs_fresh)
lemma fresh_psubst_Ctxt:
fixes X::"tvar"
and \<theta>::"Subst"
and \<Gamma>::"Ctxt"
assumes asms: "X\<sharp>\<theta>" "X\<sharp>\<Gamma>"
shows "X\<sharp>\<theta><\<Gamma>>"
using asms
by (induct \<Gamma>)
(auto simp add: fresh_psubst_tyS fresh_list_cons)
lemma subst_freshfact2_ty:
fixes X::"tvar"
and Y::"tvar"
and T::"ty"
assumes asms: "X\<sharp>S"
shows "X\<sharp>T[X::=S]"
using asms
by (nominal_induct T rule: ty.strong_induct)
(auto simp add: fresh_atm)
text \<open>instance of a type scheme\<close>
inductive
inst :: "ty \<Rightarrow> tyS \<Rightarrow> bool"("_ \<prec> _" [50,51] 50)
where
I_Ty[intro]: "T \<prec> (Ty T)"
| I_All[intro]: "\<lbrakk>X\<sharp>T'; T \<prec> S\<rbrakk> \<Longrightarrow> T[X::=T'] \<prec> \<forall>[X].S"
equivariance inst[tvar]
nominal_inductive inst
by (simp_all add: abs_fresh subst_freshfact2_ty)
lemma subst_forget_ty:
fixes T::"ty"
and X::"tvar"
assumes a: "X\<sharp>T"
shows "T[X::=S] = T"
using a
by (nominal_induct T rule: ty.strong_induct)
(auto simp add: fresh_atm)
lemma psubst_ty_lemma:
fixes \<theta>::"Subst"
and X::"tvar"
and T'::"ty"
and T::"ty"
assumes a: "X\<sharp>\<theta>"
shows "\<theta><T[X::=T']> = (\<theta><T>)[X::=\<theta><T'>]"
using a
apply(nominal_induct T avoiding: \<theta> X T' rule: ty.strong_induct)
apply(auto simp add: ty.inject lookup_fresh)
apply(rule sym)
apply(rule subst_forget_ty)
apply(rule fresh_lookup)
apply(simp_all add: fresh_atm)
done
lemma general_preserved:
fixes \<theta>::"Subst"
assumes a: "T \<prec> S"
shows "\<theta><T> \<prec> \<theta><S>"
using a
apply(nominal_induct T S avoiding: \<theta> rule: inst.strong_induct)
apply(auto)[1]
apply(simp add: psubst_ty_lemma)
apply(rule_tac I_All)
apply(simp add: fresh_psubst_ty)
apply(simp)
done
text\<open>typing judgements\<close>
inductive
typing :: "Ctxt \<Rightarrow> trm \<Rightarrow> ty \<Rightarrow> bool" (" _ \<turnstile> _ : _ " [60,60,60] 60)
where
T_VAR[intro]: "\<lbrakk>valid \<Gamma>; (x,S)\<in>set \<Gamma>; T \<prec> S\<rbrakk>\<Longrightarrow> \<Gamma> \<turnstile> Var x : T"
| T_APP[intro]: "\<lbrakk>\<Gamma> \<turnstile> t\<^sub>1 : T\<^sub>1\<rightarrow>T\<^sub>2; \<Gamma> \<turnstile> t\<^sub>2 : T\<^sub>1\<rbrakk>\<Longrightarrow> \<Gamma> \<turnstile> App t\<^sub>1 t\<^sub>2 : T\<^sub>2"
| T_LAM[intro]: "\<lbrakk>x\<sharp>\<Gamma>;((x,Ty T\<^sub>1)#\<Gamma>) \<turnstile> t : T\<^sub>2\<rbrakk> \<Longrightarrow> \<Gamma> \<turnstile> Lam [x].t : T\<^sub>1\<rightarrow>T\<^sub>2"
| T_LET[intro]: "\<lbrakk>x\<sharp>\<Gamma>; \<Gamma> \<turnstile> t\<^sub>1 : T\<^sub>1; ((x,close \<Gamma> T\<^sub>1)#\<Gamma>) \<turnstile> t\<^sub>2 : T\<^sub>2; set (ftv T\<^sub>1 - ftv \<Gamma>) \<sharp>* T\<^sub>2\<rbrakk>
\<Longrightarrow> \<Gamma> \<turnstile> Let x be t\<^sub>1 in t\<^sub>2 : T\<^sub>2"
equivariance typing[tvar]
lemma fresh_tvar_trm:
fixes X::"tvar"
and t::"trm"
shows "X\<sharp>t"
by (nominal_induct t rule: trm.strong_induct)
(simp_all add: fresh_atm abs_fresh)
lemma ftv_ty:
fixes T::"ty"
shows "supp T = set (ftv T)"
by (nominal_induct T rule: ty.strong_induct)
(simp_all add: ty.supp supp_atm)
lemma ftv_tyS:
fixes S::"tyS"
shows "supp S = set (ftv S)"
by (nominal_induct S rule: tyS.strong_induct)
(auto simp add: tyS.supp abs_supp ftv_ty)
lemma ftv_Ctxt:
fixes \<Gamma>::"Ctxt"
shows "supp \<Gamma> = set (ftv \<Gamma>)"
apply (induct \<Gamma>)
apply (simp_all add: supp_list_nil supp_list_cons)
apply (rename_tac a \<Gamma>')
apply (case_tac a)
apply (simp add: supp_prod supp_atm ftv_tyS)
done
lemma ftv_tvars:
fixes Tvs::"tvar list"
shows "supp Tvs = set Tvs"
by (induct Tvs)
(simp_all add: supp_list_nil supp_list_cons supp_atm)
lemma difference_supp:
fixes xs ys::"tvar list"
shows "((supp (xs - ys))::tvar set) = supp xs - supp ys"
by (induct xs)
(auto simp add: supp_list_nil supp_list_cons ftv_tvars)
lemma set_supp_eq:
fixes xs::"tvar list"
shows "set xs = supp xs"
by (induct xs)
(simp_all add: supp_list_nil supp_list_cons supp_atm)
nominal_inductive2 typing
avoids T_LET: "set (ftv T\<^sub>1 - ftv \<Gamma>)"
apply (simp add: fresh_star_def fresh_def ftv_Ctxt)
apply (simp add: fresh_star_def fresh_tvar_trm)
apply assumption
apply simp
done
lemma perm_fresh_fresh_aux:
"\<forall>(x,y)\<in>set (pi::tvar prm). x \<sharp> z \<and> y \<sharp> z \<Longrightarrow> pi \<bullet> (z::'a::pt_tvar) = z"
apply (induct pi rule: rev_induct)
apply simp
apply (simp add: split_paired_all pt_tvar2)
apply (frule_tac x="(a, b)" in bspec)
apply simp
apply (simp add: perm_fresh_fresh)
done
lemma freshs_mem:
fixes S::"tvar set"
assumes "x \<in> S"
and "S \<sharp>* z"
shows "x \<sharp> z"
using assms by (simp add: fresh_star_def)
lemma fresh_gen_set:
fixes X::"tvar"
and Xs::"tvar list"
assumes asm: "X\<in>set Xs"
shows "X\<sharp>gen T Xs"
using asm
apply(induct Xs)
apply(simp)
apply(rename_tac a Xs')
apply(case_tac "X=a")
apply(simp add: abs_fresh)
apply(simp add: abs_fresh)
done
lemma close_fresh:
fixes \<Gamma>::"Ctxt"
shows "\<forall>(X::tvar)\<in>set ((ftv T) - (ftv \<Gamma>)). X\<sharp>(close \<Gamma> T)"
by (simp add: fresh_gen_set)
lemma gen_supp:
shows "(supp (gen T Xs)::tvar set) = supp T - supp Xs"
by (induct Xs)
(auto simp add: supp_list_nil supp_list_cons tyS.supp abs_supp supp_atm)
lemma minus_Int_eq:
shows "T - (T - U) = T \<inter> U"
by blast
lemma close_supp:
shows "supp (close \<Gamma> T) = set (ftv T) \<inter> set (ftv \<Gamma>)"
apply (simp add: gen_supp difference_supp ftv_ty ftv_Ctxt)
apply (simp only: set_supp_eq minus_Int_eq)
done
lemma better_T_LET:
assumes x: "x\<sharp>\<Gamma>"
and t1: "\<Gamma> \<turnstile> t\<^sub>1 : T\<^sub>1"
and t2: "((x,close \<Gamma> T\<^sub>1)#\<Gamma>) \<turnstile> t\<^sub>2 : T\<^sub>2"
shows "\<Gamma> \<turnstile> Let x be t\<^sub>1 in t\<^sub>2 : T\<^sub>2"
proof -
have fin: "finite (set (ftv T\<^sub>1 - ftv \<Gamma>))" by simp
obtain pi where pi1: "(pi \<bullet> set (ftv T\<^sub>1 - ftv \<Gamma>)) \<sharp>* (T\<^sub>2, \<Gamma>)"
and pi2: "set pi \<subseteq> set (ftv T\<^sub>1 - ftv \<Gamma>) \<times> (pi \<bullet> set (ftv T\<^sub>1 - ftv \<Gamma>))"
by (rule at_set_avoiding [OF at_tvar_inst fin fs_tvar1, of "(T\<^sub>2, \<Gamma>)"])
from pi1 have pi1': "(pi \<bullet> set (ftv T\<^sub>1 - ftv \<Gamma>)) \<sharp>* \<Gamma>"
by (simp add: fresh_star_prod)
have Gamma_fresh: "\<forall>(x,y)\<in>set pi. x \<sharp> \<Gamma> \<and> y \<sharp> \<Gamma>"
apply (rule ballI)
apply (simp add: split_paired_all)
apply (drule subsetD [OF pi2])
apply (erule SigmaE)
apply (drule freshs_mem [OF _ pi1'])
apply (simp add: ftv_Ctxt [symmetric] fresh_def)
done
have close_fresh': "\<forall>(x, y)\<in>set pi. x \<sharp> close \<Gamma> T\<^sub>1 \<and> y \<sharp> close \<Gamma> T\<^sub>1"
apply (rule ballI)
apply (simp add: split_paired_all)
apply (drule subsetD [OF pi2])
apply (erule SigmaE)
apply (drule bspec [OF close_fresh])
apply (drule freshs_mem [OF _ pi1'])
apply (simp add: fresh_def close_supp ftv_Ctxt)
done
note x
moreover from Gamma_fresh perm_boolI [OF t1, of pi]
have "\<Gamma> \<turnstile> t\<^sub>1 : pi \<bullet> T\<^sub>1"
by (simp add: perm_fresh_fresh_aux eqvts fresh_tvar_trm)
moreover from t2 close_fresh'
have "(x,(pi \<bullet> close \<Gamma> T\<^sub>1))#\<Gamma> \<turnstile> t\<^sub>2 : T\<^sub>2"
by (simp add: perm_fresh_fresh_aux)
with Gamma_fresh have "(x,close \<Gamma> (pi \<bullet> T\<^sub>1))#\<Gamma> \<turnstile> t\<^sub>2 : T\<^sub>2"
by (simp add: close_eqvt perm_fresh_fresh_aux)
moreover from pi1 Gamma_fresh
have "set (ftv (pi \<bullet> T\<^sub>1) - ftv \<Gamma>) \<sharp>* T\<^sub>2"
by (simp only: eqvts fresh_star_prod perm_fresh_fresh_aux)
ultimately show ?thesis by (rule T_LET)
qed
lemma ftv_ty_subst:
fixes T::"ty"
and \<theta>::"Subst"
and X Y ::"tvar"
assumes a1: "X \<in> set (ftv T)"
and a2: "Y \<in> set (ftv (lookup \<theta> X))"
shows "Y \<in> set (ftv (\<theta><T>))"
using a1 a2
by (nominal_induct T rule: ty.strong_induct) (auto)
lemma ftv_tyS_subst:
fixes S::"tyS"
and \<theta>::"Subst"
and X Y::"tvar"
assumes a1: "X \<in> set (ftv S)"
and a2: "Y \<in> set (ftv (lookup \<theta> X))"
shows "Y \<in> set (ftv (\<theta><S>))"
using a1 a2
by (nominal_induct S avoiding: \<theta> Y rule: tyS.strong_induct)
(auto simp add: ftv_ty_subst fresh_atm)
lemma ftv_Ctxt_subst:
fixes \<Gamma>::"Ctxt"
and \<theta>::"Subst"
assumes a1: "X \<in> set (ftv \<Gamma>)"
and a2: "Y \<in> set (ftv (lookup \<theta> X))"
shows "Y \<in> set (ftv (\<theta><\<Gamma>>))"
using a1 a2
by (induct \<Gamma>)
(auto simp add: ftv_tyS_subst)
lemma gen_preserved1:
assumes asm: "Xs \<sharp>* \<theta>"
shows "\<theta><gen T Xs> = gen (\<theta><T>) Xs"
using asm
by (induct Xs)
(auto simp add: fresh_star_def)
lemma gen_preserved2:
fixes T::"ty"
and \<Gamma>::"Ctxt"
assumes asm: "((ftv T) - (ftv \<Gamma>)) \<sharp>* \<theta>"
shows "((ftv (\<theta><T>)) - (ftv (\<theta><\<Gamma>>))) = ((ftv T) - (ftv \<Gamma>))"
using asm
apply(nominal_induct T rule: ty.strong_induct)
apply(auto simp add: fresh_star_def)
apply(simp add: lookup_fresh)
apply(simp add: ftv_Ctxt[symmetric])
apply(fold fresh_def)
apply(rule fresh_psubst_Ctxt)
apply(assumption)
apply(assumption)
apply(rule difference_supset)
apply(auto)
apply(simp add: ftv_Ctxt_subst)
done
lemma close_preserved:
fixes \<Gamma>::"Ctxt"
assumes asm: "((ftv T) - (ftv \<Gamma>)) \<sharp>* \<theta>"
shows "\<theta><close \<Gamma> T> = close (\<theta><\<Gamma>>) (\<theta><T>)"
using asm
by (simp add: gen_preserved1 gen_preserved2)
lemma var_fresh_for_ty:
fixes x::"var"
and T::"ty"
shows "x\<sharp>T"
by (nominal_induct T rule: ty.strong_induct)
(simp_all add: fresh_atm)
lemma var_fresh_for_tyS:
fixes x::"var"
and S::"tyS"
shows "x\<sharp>S"
by (nominal_induct S rule: tyS.strong_induct)
(simp_all add: abs_fresh var_fresh_for_ty)
lemma psubst_fresh_Ctxt:
fixes x::"var"
and \<Gamma>::"Ctxt"
and \<theta>::"Subst"
shows "x\<sharp>\<theta><\<Gamma>> = x\<sharp>\<Gamma>"
by (induct \<Gamma>)
(auto simp add: fresh_list_cons fresh_list_nil fresh_prod var_fresh_for_tyS)
lemma psubst_valid:
fixes \<theta>::Subst
and \<Gamma>::Ctxt
assumes a: "valid \<Gamma>"
shows "valid (\<theta><\<Gamma>>)"
using a
by (induct)
(auto simp add: psubst_fresh_Ctxt)
lemma psubst_in:
fixes \<Gamma>::"Ctxt"
and \<theta>::"Subst"
and pi::"tvar prm"
and S::"tyS"
assumes a: "(x,S)\<in>set \<Gamma>"
shows "(x,\<theta><S>)\<in>set (\<theta><\<Gamma>>)"
using a
by (induct \<Gamma>)
(auto simp add: calc_atm)
lemma typing_preserved:
fixes \<theta>::"Subst"
and pi::"tvar prm"
assumes a: "\<Gamma> \<turnstile> t : T"
shows "(\<theta><\<Gamma>>) \<turnstile> t : (\<theta><T>)"
using a
proof (nominal_induct \<Gamma> t T avoiding: \<theta> rule: typing.strong_induct)
case (T_VAR \<Gamma> x S T)
have a1: "valid \<Gamma>" by fact
have a2: "(x, S) \<in> set \<Gamma>" by fact
have a3: "T \<prec> S" by fact
have "valid (\<theta><\<Gamma>>)" using a1 by (simp add: psubst_valid)
moreover
have "(x,\<theta><S>)\<in>set (\<theta><\<Gamma>>)" using a2 by (simp add: psubst_in)
moreover
have "\<theta><T> \<prec> \<theta><S>" using a3 by (simp add: general_preserved)
ultimately show "(\<theta><\<Gamma>>) \<turnstile> Var x : (\<theta><T>)" by (simp add: typing.T_VAR)
next
case (T_APP \<Gamma> t1 T1 T2 t2)
have "\<theta><\<Gamma>> \<turnstile> t1 : \<theta><T1 \<rightarrow> T2>" by fact
then have "\<theta><\<Gamma>> \<turnstile> t1 : (\<theta><T1>) \<rightarrow> (\<theta><T2>)" by simp
moreover
have "\<theta><\<Gamma>> \<turnstile> t2 : \<theta><T1>" by fact
ultimately show "\<theta><\<Gamma>> \<turnstile> App t1 t2 : \<theta><T2>" by (simp add: typing.T_APP)
next
case (T_LAM x \<Gamma> T1 t T2)
fix pi::"tvar prm" and \<theta>::"Subst"
have "x\<sharp>\<Gamma>" by fact
then have "x\<sharp>\<theta><\<Gamma>>" by (simp add: psubst_fresh_Ctxt)
moreover
have "\<theta><((x, Ty T1)#\<Gamma>)> \<turnstile> t : \<theta><T2>" by fact
then have "((x, Ty (\<theta><T1>))#(\<theta><\<Gamma>>)) \<turnstile> t : \<theta><T2>" by (simp add: calc_atm)
ultimately show "\<theta><\<Gamma>> \<turnstile> Lam [x].t : \<theta><T1 \<rightarrow> T2>" by (simp add: typing.T_LAM)
next
case (T_LET x \<Gamma> t1 T1 t2 T2)
have vc: "((ftv T1) - (ftv \<Gamma>)) \<sharp>* \<theta>" by fact
have "x\<sharp>\<Gamma>" by fact
then have a1: "x\<sharp>\<theta><\<Gamma>>" by (simp add: calc_atm psubst_fresh_Ctxt)
have a2: "\<theta><\<Gamma>> \<turnstile> t1 : \<theta><T1>" by fact
have a3: "\<theta><((x, close \<Gamma> T1)#\<Gamma>)> \<turnstile> t2 : \<theta><T2>" by fact
from a2 a3 show "\<theta><\<Gamma>> \<turnstile> Let x be t1 in t2 : \<theta><T2>"
apply -
apply(rule better_T_LET)
apply(rule a1)
apply(rule a2)
apply(simp add: close_preserved vc)
done
qed
end