--- /dev/null
+(**************************************************************************)
+(* ___ *)
+(* ||M|| *)
+(* ||A|| A project by Andrea Asperti *)
+(* ||T|| *)
+(* ||I|| Developers: *)
+(* ||T|| The HELM team. *)
+(* ||A|| http://helm.cs.unibo.it *)
+(* \ / *)
+(* \ / This file is distributed under the terms of the *)
+(* v GNU General Public License Version 2 *)
+(* *)
+(**************************************************************************)
+
+(* This file was automatically generated: do not edit *********************)
+
+set "baseuri" "cic:/matita/CoRN-Decl/reals/RealFuncts".
+
+include "CoRN.ma".
+
+(* $Id: RealFuncts.v,v 1.4 2004/04/07 15:08:10 lcf Exp $ *)
+
+include "reals/CReals1.ma".
+
+(*#* * Continuity of Functions on Reals
+*)
+
+(* begin hide *)
+
+(* UNEXPORTED
+Set Implicit Arguments.
+*)
+
+(* UNEXPORTED
+Unset Strict Implicit.
+*)
+
+(* end hide *)
+
+(* UNEXPORTED
+Section Continuity
+*)
+
+alias id "f" = "cic:/CoRN/reals/RealFuncts/Continuity/f.var".
+
+alias id "f2" = "cic:/CoRN/reals/RealFuncts/Continuity/f2.var".
+
+(*#*
+Let [f] be a unary setoid operation on [IR] and
+let [f2] be a binary setoid operation on [IR].
+
+We use the following notations for intervals. [Intclr a b] for the
+closed interval [[a,b]], [Intolr a b] for the
+open interval [(a,b)], [Intcl a] for the
+left-closed interval $[a,\infty)$#[a,∞)#, [Intol a] for the
+left-open interval $(a,\infty)$#(a,∞)#, [Intcr b] for the
+right-closed interval $(-\infty,b]$#(-∞,b]#.
+
+Intervals like $[a,b]$#[a,b]# are defined for arbitrary reals [a,b] (being
+$\emptyset$#∅# for [a [>] b]).
+*)
+
+inline "cic:/CoRN/reals/RealFuncts/Intclr.con".
+
+inline "cic:/CoRN/reals/RealFuncts/Intolr.con".
+
+inline "cic:/CoRN/reals/RealFuncts/Intol.con".
+
+inline "cic:/CoRN/reals/RealFuncts/Intcl.con".
+
+inline "cic:/CoRN/reals/RealFuncts/Intcr.con".
+
+(*#* The limit of [f(x)] as [x] goes to [p = l], for both unary and binary
+functions:
+
+The limit of [f] in [p] is [l] if
+[[
+forall e [>] Zero, exists d [>] Zero, forall (x : IR)
+( [--]d [<] p[-]x [<] d) -> ( [--]e [<] [--]f(x) [<] e)
+]]
+*)
+
+inline "cic:/CoRN/reals/RealFuncts/funLim.con".
+
+(*#* The definition of limit of [f] in [p] using Cauchy sequences. *)
+
+inline "cic:/CoRN/reals/RealFuncts/funLim_Cauchy.con".
+
+(*#* The first definition implies the second one. *)
+
+(*
+ Ax_iom funLim_prop1 :(p,l:IR)(funLim p l)->(funLim_Cauchy p l).
+Intros. Unfold funLim_Cauchy. Unfold funLim in H. Intros.
+Elim (H e H1). Intros.
+Elim s. Intros s_seq s_proof.
+Decompose [and] H2.
+Cut (Zero [<] x[/]TwoNZ).
+Intro Hx2.
+Elim (s_proof (x[/]TwoNZ) Hx2).
+Intros N HN.
+Exists N.
+Intros.
+Apply AbsSmall_minus.
+Apply H5.
+Generalize (HN m H3).
+Intro HmN.
+*)
+
+(*#* The limit of [f] in [(p,p')] is [l] if
+[[
+forall e [>] Zero, exists d [>] Zero, forall (x : IR)
+( [--]d [<] p[-]x [<] d) -> ( [--]d' [<] p'[-]y [<] d') -> ( [--]e [<] l[-]f(x,y) [<] e
+]]
+*)
+
+inline "cic:/CoRN/reals/RealFuncts/funLim2.con".
+
+(*#* The function [f] is continuous at [p] if the limit of [f(x)] as
+[x] goes to [p] is [f(p)]. This is the [eps [/] delta] definition.
+We also give the definition with limits of Cauchy sequences.
+*)
+
+inline "cic:/CoRN/reals/RealFuncts/continAt.con".
+
+inline "cic:/CoRN/reals/RealFuncts/continAtCauchy.con".
+
+inline "cic:/CoRN/reals/RealFuncts/continAt2.con".
+
+(*
+Ax_iom continAt_prop1 :(p:IR)(continAt p)->(continAtCauchy p).
+*)
+
+inline "cic:/CoRN/reals/RealFuncts/contin.con".
+
+inline "cic:/CoRN/reals/RealFuncts/continCauchy.con".
+
+inline "cic:/CoRN/reals/RealFuncts/contin2.con".
+
+(*#*
+Continuous on a closed, resp.%\% open, resp.%\% left open, resp.%\% left closed
+interval *)
+
+inline "cic:/CoRN/reals/RealFuncts/continOnc.con".
+
+inline "cic:/CoRN/reals/RealFuncts/continOno.con".
+
+inline "cic:/CoRN/reals/RealFuncts/continOnol.con".
+
+inline "cic:/CoRN/reals/RealFuncts/continOncl.con".
+
+(*
+Section Sequence_and_function_limits.
+
+_**
+If $\lim_{x->p} (f x) = l$, then for every sequence $p_n$ whose
+limit is $p$, $\lim_{n->\infty} f (p_n) =l$.
+ *_
+
+Lemma funLim_SeqLimit:
+ (p,l:IR)(fl:(funLim p l))
+ (pn:nat->IR)(sl:(SeqLimit pn p)) (SeqLimit ( [n:nat] (f (pn n))) l).
+Proof.
+Intros; Unfold seqLimit.
+Intros eps epos.
+Elim (fl ? epos); Intros del dh; Elim dh; Intros H0 H1.
+Elim (sl ? H0); Intros N Nh.
+Exists N. Intros m leNm.
+Apply AbsSmall_minus.
+Apply H1.
+Apply AbsSmall_minus.
+Apply (Nh ? leNm).
+Qed.
+
+_**** Is the converse constructively provable? **
+Lemma SeqLimit_funLim:
+ (p,l:IR)((pn:nat->IR)(sl:(SeqLimit pn p)) (SeqLimit ( [n:nat] (f (pn n))) l))->
+ (funLim p l).
+****_
+
+_**
+Now the same Lemma in terms of Cauchy sequences: if $\lim_{x->p} (f x) = l$,
+then for every Cauchy sequence $s_n$ whose
+limit is $p$, $\lim_{n->\infty} f (s_n) =l$.
+ *_
+
+Ax_iom funLim_isCauchy:
+ (p,l:IR)(funLim p l)->(s:CauchySeqR)((Lim s) [=] p)->
+ (e:IR)(Zero [<] e)->(Ex [N:nat] (m:nat)(le N m)
+ ->(AbsSmall e ((s m) [-] (s N)))).
+
+End Sequence_and_function_limits.
+
+Section Monotonic_functions.
+
+Definition str_monot := (x,y:IR)(x [<] y)->((f x) [<] (f y)).
+
+Definition str_monotOnc := [a,b:IR]
+ (x,y:IR)(Intclr a b x)->(Intclr a b y)
+ ->(x [<] y)->((f x) [<] (f y)).
+
+Definition str_monotOncl := [a:IR]
+ (x,y:IR)(Intcl a x)->(Intcl a y)
+ ->(x [<] y)->((f x) [<] (f y)).
+
+Definition str_monotOnol := [a:IR]
+ (x,y:IR)(Intol a x)->(Intol a y)
+ ->(x [<] y)->((f x) [<] (f y)).
+
+_** Following probably not needed for the FTA proof;
+it stated that strong monotonicity on a closed interval implies that the
+intermediate value theorem holds on this interval. For FTA we need IVT on
+$[0,\infty>$.
+*_
+
+Ax_iom strmonc_imp_ivt :(a,b:IR)(str_monotOnc a b)
+ ->(x,y:IR)(x [<] y)->(Intclr a b x)->(Intclr a b y)
+ ->((f x) [<] Zero)->(Zero [<] (f y))
+ ->(EX z:IR | (Intclr x y z)/\((f z) [=] Zero)).
+_**
+$\forall c\in\RR (f\mbox{ strongly monotonic on }[c,\infty>)
+\rightarrow \forall a,b\in\RR(c <a)\rightarrow( c< b)\rightarrow\ (f (a)<0)
+\rightarrow\ (0:<f(b))
+ \rightarrow \forall x,y\in\RR (a\leq x\leq b)\rightarrow
+ (a\leq y\leq b)\rightarrow (x<y)
+ \rightarrow \exists z\in\RR(x\leq z\leq y)\wedge(f(z)\noto 0))$
+*_
+
+Ax_iom strmon_ivt_prem : (c:IR)(str_monotOncl c)->
+ (a,b:IR)(Intcl c a)->(Intcl c b)->((f a) [<] Zero)->(Zero [<] (f b))
+ ->(x,y:IR)(Intclr a b x)->(Intclr a b y)->(x [<] y)
+ ->(EX z:IR | (Intclr x y z)/\((f z) [#] Zero)).
+
+_** The following is lemma 5.8 from the skeleton
+
+$\forall c\in\RR (f\mbox{ strongly monotonic on }[c,\infty>)
+\rightarrow \forall a,b\in\RR(a<b) \rightarrow(c <a)\rightarrow( c< b)
+\rightarrow(f (a)<0)\rightarrow (0:<f(b))
+ \rightarrow \exists z\in\RR(a\leq z\leq b)\wedge(f(z)= 0))$
+*_
+
+Ax_iom strmoncl_imp_ivt : (c:IR)(str_monotOncl c)
+ ->(a,b:IR)(a [<] b)->(Intcl c a)->(Intcl c b)
+ ->((f a) [<] Zero)->(Zero [<] (f b))
+ ->(EX z:IR | (Intclr a b z)/\ ((f z) [=] Zero)).
+End Monotonic_functions.
+
+*)
+
+(* UNEXPORTED
+End Continuity
+*)
+
+(* begin hide *)
+
+(* UNEXPORTED
+Set Strict Implicit.
+*)
+
+(* UNEXPORTED
+Unset Implicit Arguments.
+*)
+
+(* end hide *)
+
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