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