--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/NSA/Star.thy Thu Jul 03 17:47:22 2008 +0200
@@ -0,0 +1,348 @@
+(* Title : Star.thy
+ Author : Jacques D. Fleuriot
+ Copyright : 1998 University of Cambridge
+ Conversion to Isar and new proofs by Lawrence C Paulson, 2003/4
+*)
+
+header{*Star-Transforms in Non-Standard Analysis*}
+
+theory Star
+imports NSA
+begin
+
+definition
+ (* internal sets *)
+ starset_n :: "(nat => 'a set) => 'a star set" ("*sn* _" [80] 80) where
+ "*sn* As = Iset (star_n As)"
+
+definition
+ InternalSets :: "'a star set set" where
+ [code func del]: "InternalSets = {X. \<exists>As. X = *sn* As}"
+
+definition
+ (* nonstandard extension of function *)
+ is_starext :: "['a star => 'a star, 'a => 'a] => bool" where
+ [code func del]: "is_starext F f = (\<forall>x y. \<exists>X \<in> Rep_star(x). \<exists>Y \<in> Rep_star(y).
+ ((y = (F x)) = ({n. Y n = f(X n)} : FreeUltrafilterNat)))"
+
+definition
+ (* internal functions *)
+ starfun_n :: "(nat => ('a => 'b)) => 'a star => 'b star" ("*fn* _" [80] 80) where
+ "*fn* F = Ifun (star_n F)"
+
+definition
+ InternalFuns :: "('a star => 'b star) set" where
+ [code func del]:"InternalFuns = {X. \<exists>F. X = *fn* F}"
+
+
+(*--------------------------------------------------------
+ Preamble - Pulling "EX" over "ALL"
+ ---------------------------------------------------------*)
+
+(* This proof does not need AC and was suggested by the
+ referee for the JCM Paper: let f(x) be least y such
+ that Q(x,y)
+*)
+lemma no_choice: "\<forall>x. \<exists>y. Q x y ==> \<exists>(f :: 'a => nat). \<forall>x. Q x (f x)"
+apply (rule_tac x = "%x. LEAST y. Q x y" in exI)
+apply (blast intro: LeastI)
+done
+
+subsection{*Properties of the Star-transform Applied to Sets of Reals*}
+
+lemma STAR_star_of_image_subset: "star_of ` A <= *s* A"
+by auto
+
+lemma STAR_hypreal_of_real_Int: "*s* X Int Reals = hypreal_of_real ` X"
+by (auto simp add: SReal_def)
+
+lemma STAR_star_of_Int: "*s* X Int Standard = star_of ` X"
+by (auto simp add: Standard_def)
+
+lemma lemma_not_hyprealA: "x \<notin> hypreal_of_real ` A ==> \<forall>y \<in> A. x \<noteq> hypreal_of_real y"
+by auto
+
+lemma lemma_not_starA: "x \<notin> star_of ` A ==> \<forall>y \<in> A. x \<noteq> star_of y"
+by auto
+
+lemma lemma_Compl_eq: "- {n. X n = xa} = {n. X n \<noteq> xa}"
+by auto
+
+lemma STAR_real_seq_to_hypreal:
+ "\<forall>n. (X n) \<notin> M ==> star_n X \<notin> *s* M"
+apply (unfold starset_def star_of_def)
+apply (simp add: Iset_star_n)
+done
+
+lemma STAR_singleton: "*s* {x} = {star_of x}"
+by simp
+
+lemma STAR_not_mem: "x \<notin> F ==> star_of x \<notin> *s* F"
+by transfer
+
+lemma STAR_subset_closed: "[| x : *s* A; A <= B |] ==> x : *s* B"
+by (erule rev_subsetD, simp)
+
+text{*Nonstandard extension of a set (defined using a constant
+ sequence) as a special case of an internal set*}
+
+lemma starset_n_starset: "\<forall>n. (As n = A) ==> *sn* As = *s* A"
+apply (drule expand_fun_eq [THEN iffD2])
+apply (simp add: starset_n_def starset_def star_of_def)
+done
+
+
+(*----------------------------------------------------------------*)
+(* Theorems about nonstandard extensions of functions *)
+(*----------------------------------------------------------------*)
+
+(*----------------------------------------------------------------*)
+(* Nonstandard extension of a function (defined using a *)
+(* constant sequence) as a special case of an internal function *)
+(*----------------------------------------------------------------*)
+
+lemma starfun_n_starfun: "\<forall>n. (F n = f) ==> *fn* F = *f* f"
+apply (drule expand_fun_eq [THEN iffD2])
+apply (simp add: starfun_n_def starfun_def star_of_def)
+done
+
+
+(*
+ Prove that abs for hypreal is a nonstandard extension of abs for real w/o
+ use of congruence property (proved after this for general
+ nonstandard extensions of real valued functions).
+
+ Proof now Uses the ultrafilter tactic!
+*)
+
+lemma hrabs_is_starext_rabs: "is_starext abs abs"
+apply (simp add: is_starext_def, safe)
+apply (rule_tac x=x in star_cases)
+apply (rule_tac x=y in star_cases)
+apply (unfold star_n_def, auto)
+apply (rule bexI, rule_tac [2] lemma_starrel_refl)
+apply (rule bexI, rule_tac [2] lemma_starrel_refl)
+apply (fold star_n_def)
+apply (unfold star_abs_def starfun_def star_of_def)
+apply (simp add: Ifun_star_n star_n_eq_iff)
+done
+
+text{*Nonstandard extension of functions*}
+
+lemma starfun:
+ "( *f* f) (star_n X) = star_n (%n. f (X n))"
+by (rule starfun_star_n)
+
+lemma starfun_if_eq:
+ "!!w. w \<noteq> star_of x
+ ==> ( *f* (\<lambda>z. if z = x then a else g z)) w = ( *f* g) w"
+by (transfer, simp)
+
+(*-------------------------------------------
+ multiplication: ( *f) x ( *g) = *(f x g)
+ ------------------------------------------*)
+lemma starfun_mult: "!!x. ( *f* f) x * ( *f* g) x = ( *f* (%x. f x * g x)) x"
+by (transfer, rule refl)
+declare starfun_mult [symmetric, simp]
+
+(*---------------------------------------
+ addition: ( *f) + ( *g) = *(f + g)
+ ---------------------------------------*)
+lemma starfun_add: "!!x. ( *f* f) x + ( *f* g) x = ( *f* (%x. f x + g x)) x"
+by (transfer, rule refl)
+declare starfun_add [symmetric, simp]
+
+(*--------------------------------------------
+ subtraction: ( *f) + -( *g) = *(f + -g)
+ -------------------------------------------*)
+lemma starfun_minus: "!!x. - ( *f* f) x = ( *f* (%x. - f x)) x"
+by (transfer, rule refl)
+declare starfun_minus [symmetric, simp]
+
+(*FIXME: delete*)
+lemma starfun_add_minus: "!!x. ( *f* f) x + -( *f* g) x = ( *f* (%x. f x + -g x)) x"
+by (transfer, rule refl)
+declare starfun_add_minus [symmetric, simp]
+
+lemma starfun_diff: "!!x. ( *f* f) x - ( *f* g) x = ( *f* (%x. f x - g x)) x"
+by (transfer, rule refl)
+declare starfun_diff [symmetric, simp]
+
+(*--------------------------------------
+ composition: ( *f) o ( *g) = *(f o g)
+ ---------------------------------------*)
+
+lemma starfun_o2: "(%x. ( *f* f) (( *f* g) x)) = *f* (%x. f (g x))"
+by (transfer, rule refl)
+
+lemma starfun_o: "( *f* f) o ( *f* g) = ( *f* (f o g))"
+by (transfer o_def, rule refl)
+
+text{*NS extension of constant function*}
+lemma starfun_const_fun [simp]: "!!x. ( *f* (%x. k)) x = star_of k"
+by (transfer, rule refl)
+
+text{*the NS extension of the identity function*}
+
+lemma starfun_Id [simp]: "!!x. ( *f* (%x. x)) x = x"
+by (transfer, rule refl)
+
+(* this is trivial, given starfun_Id *)
+lemma starfun_Idfun_approx:
+ "x @= star_of a ==> ( *f* (%x. x)) x @= star_of a"
+by (simp only: starfun_Id)
+
+text{*The Star-function is a (nonstandard) extension of the function*}
+
+lemma is_starext_starfun: "is_starext ( *f* f) f"
+apply (simp add: is_starext_def, auto)
+apply (rule_tac x = x in star_cases)
+apply (rule_tac x = y in star_cases)
+apply (auto intro!: bexI [OF _ Rep_star_star_n]
+ simp add: starfun star_n_eq_iff)
+done
+
+text{*Any nonstandard extension is in fact the Star-function*}
+
+lemma is_starfun_starext: "is_starext F f ==> F = *f* f"
+apply (simp add: is_starext_def)
+apply (rule ext)
+apply (rule_tac x = x in star_cases)
+apply (drule_tac x = x in spec)
+apply (drule_tac x = "( *f* f) x" in spec)
+apply (auto simp add: starfun_star_n)
+apply (simp add: star_n_eq_iff [symmetric])
+apply (simp add: starfun_star_n [of f, symmetric])
+done
+
+lemma is_starext_starfun_iff: "(is_starext F f) = (F = *f* f)"
+by (blast intro: is_starfun_starext is_starext_starfun)
+
+text{*extented function has same solution as its standard
+ version for real arguments. i.e they are the same
+ for all real arguments*}
+lemma starfun_eq: "( *f* f) (star_of a) = star_of (f a)"
+by (rule starfun_star_of)
+
+lemma starfun_approx: "( *f* f) (star_of a) @= star_of (f a)"
+by simp
+
+(* useful for NS definition of derivatives *)
+lemma starfun_lambda_cancel:
+ "!!x'. ( *f* (%h. f (x + h))) x' = ( *f* f) (star_of x + x')"
+by (transfer, rule refl)
+
+lemma starfun_lambda_cancel2:
+ "( *f* (%h. f(g(x + h)))) x' = ( *f* (f o g)) (star_of x + x')"
+by (unfold o_def, rule starfun_lambda_cancel)
+
+lemma starfun_mult_HFinite_approx:
+ fixes l m :: "'a::real_normed_algebra star"
+ shows "[| ( *f* f) x @= l; ( *f* g) x @= m;
+ l: HFinite; m: HFinite
+ |] ==> ( *f* (%x. f x * g x)) x @= l * m"
+apply (drule (3) approx_mult_HFinite)
+apply (auto intro: approx_HFinite [OF _ approx_sym])
+done
+
+lemma starfun_add_approx: "[| ( *f* f) x @= l; ( *f* g) x @= m
+ |] ==> ( *f* (%x. f x + g x)) x @= l + m"
+by (auto intro: approx_add)
+
+text{*Examples: hrabs is nonstandard extension of rabs
+ inverse is nonstandard extension of inverse*}
+
+(* can be proved easily using theorem "starfun" and *)
+(* properties of ultrafilter as for inverse below we *)
+(* use the theorem we proved above instead *)
+
+lemma starfun_rabs_hrabs: "*f* abs = abs"
+by (simp only: star_abs_def)
+
+lemma starfun_inverse_inverse [simp]: "( *f* inverse) x = inverse(x)"
+by (simp only: star_inverse_def)
+
+lemma starfun_inverse: "!!x. inverse (( *f* f) x) = ( *f* (%x. inverse (f x))) x"
+by (transfer, rule refl)
+declare starfun_inverse [symmetric, simp]
+
+lemma starfun_divide: "!!x. ( *f* f) x / ( *f* g) x = ( *f* (%x. f x / g x)) x"
+by (transfer, rule refl)
+declare starfun_divide [symmetric, simp]
+
+lemma starfun_inverse2: "!!x. inverse (( *f* f) x) = ( *f* (%x. inverse (f x))) x"
+by (transfer, rule refl)
+
+text{*General lemma/theorem needed for proofs in elementary
+ topology of the reals*}
+lemma starfun_mem_starset:
+ "!!x. ( *f* f) x : *s* A ==> x : *s* {x. f x \<in> A}"
+by (transfer, simp)
+
+text{*Alternative definition for hrabs with rabs function
+ applied entrywise to equivalence class representative.
+ This is easily proved using starfun and ns extension thm*}
+lemma hypreal_hrabs:
+ "abs (star_n X) = star_n (%n. abs (X n))"
+by (simp only: starfun_rabs_hrabs [symmetric] starfun)
+
+text{*nonstandard extension of set through nonstandard extension
+ of rabs function i.e hrabs. A more general result should be
+ where we replace rabs by some arbitrary function f and hrabs
+ by its NS extenson. See second NS set extension below.*}
+lemma STAR_rabs_add_minus:
+ "*s* {x. abs (x + - y) < r} =
+ {x. abs(x + -star_of y) < star_of r}"
+by (transfer, rule refl)
+
+lemma STAR_starfun_rabs_add_minus:
+ "*s* {x. abs (f x + - y) < r} =
+ {x. abs(( *f* f) x + -star_of y) < star_of r}"
+by (transfer, rule refl)
+
+text{*Another characterization of Infinitesimal and one of @= relation.
+ In this theory since @{text hypreal_hrabs} proved here. Maybe
+ move both theorems??*}
+lemma Infinitesimal_FreeUltrafilterNat_iff2:
+ "(star_n X \<in> Infinitesimal) =
+ (\<forall>m. {n. norm(X n) < inverse(real(Suc m))}
+ \<in> FreeUltrafilterNat)"
+by (simp add: Infinitesimal_hypreal_of_nat_iff star_of_def
+ hnorm_def star_of_nat_def starfun_star_n
+ star_n_inverse star_n_less real_of_nat_def)
+
+lemma HNatInfinite_inverse_Infinitesimal [simp]:
+ "n \<in> HNatInfinite ==> inverse (hypreal_of_hypnat n) \<in> Infinitesimal"
+apply (cases n)
+apply (auto simp add: of_hypnat_def starfun_star_n real_of_nat_def [symmetric] star_n_inverse real_norm_def
+ HNatInfinite_FreeUltrafilterNat_iff
+ Infinitesimal_FreeUltrafilterNat_iff2)
+apply (drule_tac x="Suc m" in spec)
+apply (erule ultra, simp)
+done
+
+lemma approx_FreeUltrafilterNat_iff: "star_n X @= star_n Y =
+ (\<forall>r>0. {n. norm (X n - Y n) < r} : FreeUltrafilterNat)"
+apply (subst approx_minus_iff)
+apply (rule mem_infmal_iff [THEN subst])
+apply (simp add: star_n_diff)
+apply (simp add: Infinitesimal_FreeUltrafilterNat_iff)
+done
+
+lemma approx_FreeUltrafilterNat_iff2: "star_n X @= star_n Y =
+ (\<forall>m. {n. norm (X n - Y n) <
+ inverse(real(Suc m))} : FreeUltrafilterNat)"
+apply (subst approx_minus_iff)
+apply (rule mem_infmal_iff [THEN subst])
+apply (simp add: star_n_diff)
+apply (simp add: Infinitesimal_FreeUltrafilterNat_iff2)
+done
+
+lemma inj_starfun: "inj starfun"
+apply (rule inj_onI)
+apply (rule ext, rule ccontr)
+apply (drule_tac x = "star_n (%n. xa)" in fun_cong)
+apply (auto simp add: starfun star_n_eq_iff)
+done
+
+end