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15 (* This file was automatically generated: do not edit *********************)
17 set "baseuri" "cic:/matita/CoRN-Decl/ftc/MoreIntervals".
19 (* $Id: MoreIntervals.v,v 1.6 2004/04/23 10:00:59 lcf Exp $ *)
33 (*#* printing realline %\ensuremath{\RR}% #(-∞,+∞)# *)
35 (*#* printing openl %\ensuremath{(\cdot,+\infty)}% #(⋅,+∞)# *)
37 (*#* printing openr %\ensuremath{(-\infty,\cdot)}% #(-∞,⋅)# *)
39 (*#* printing closel %\ensuremath{[\cdot,+\infty)}% #[⋅,+∞)# *)
41 (*#* printing closer %\ensuremath{(-\infty,\cdot]}% #(-∞,⋅]# *)
43 (*#* printing olor %\ensuremath{(\cdot,\cdot)}% #(⋅,⋅)# *)
45 (*#* printing clor %\ensuremath{[\cdot,\cdot)}% #[⋅,⋅)# *)
47 (*#* printing olcr %\ensuremath{(\cdot,\cdot]}% #(⋅,⋅]# *)
49 (*#* printing clcr %\ensuremath{[\cdot,\cdot]}% #[⋅,⋅]# *)
51 (*#* *Generalized Intervals
53 At this stage we have enough material to begin generalizing our
54 concepts in preparation for the fundamental theorem of calculus and
55 the definition of the main (non-polynomial) functions of analysis.
57 In order to define functions via power series (or any other kind of
58 series) we need to formalize a notion of convergence more general than
59 the one we already have on compact intervals. This is necessary for
60 practical reasons: we want to define a single exponential function
61 with domain [IR], not several exponential functions defined on compact
62 intervals which we prove to be the same wherever their domains
63 overlap. In a similar way, we want to define indefinite integrals on
64 infinite domains and not only on compact intervals.
66 Unfortunately, proceeding in a way analogous to how we defined the
67 concept of global continuity will lead us nowhere; the concept turns
68 out to be to general, and the behaviour on too small domains
69 (typically intervals [[a,a']] where [a [=] a'] is neither
70 provably true nor provably false) will be unsatisfactory.
72 There is a special family of sets, however, where this problems can be
73 avoided: intervals. Intervals have some nice properties that allow us
74 to prove good results, namely the facts that if [a] and [b] are
75 elements of an interval [I] then so are [Min(a,b)] and
76 [Max(a,b)] (which is in general not true) and also the
77 compact interval [[a,b]] is included in [I]. Furthermore, all
78 intervals are characterized by simple, well defined predicates, and
79 the nonempty and proper concepts become very easy to define.
81 **Definitions and Basic Results
83 We define an inductive type of intervals with nine constructors,
84 corresponding to the nine basic types of intervals. The reason why so
85 many constructors are needed is that we do not have a notion of real
86 line, for many reasons which we will not discuss here. Also it seems
87 simple to directly define finite intervals than to define then later
88 as intersections of infinite intervals, as it would only mess things
91 The compact interval which we will define here is obviously the same
92 that we have been working with all the way through; why, then, the
93 different formulation? The reason is simple: if we had worked with
94 intervals from the beginning we would have had case definitions at
95 every spot, and our lemmas and proofs would have been very awkward.
96 Also, it seems more natural to characterize a compact interval by two
97 real numbers (and a proof) than as a particular case of a more general
98 concept which doesn't have an intuitive interpretation. Finally, the
99 definitions we will make here will have the elegant consequence that
100 from this point on we can work with any kind of intervals in exactly
104 inline cic:/CoRN/ftc/MoreIntervals/interval.ind.
107 To each interval a predicate (set) is assigned by the following map:
110 inline cic:/CoRN/ftc/MoreIntervals/iprop.con.
117 This map is made into a coercion, so that intervals
118 %\emph{%#<i>#are%}%#</i># really subsets of reals.
120 We now define what it means for an interval to be nonvoid, proper,
121 finite and compact in the obvious way.
124 inline cic:/CoRN/ftc/MoreIntervals/nonvoid.con.
126 inline cic:/CoRN/ftc/MoreIntervals/proper.con.
128 inline cic:/CoRN/ftc/MoreIntervals/finite.con.
130 inline cic:/CoRN/ftc/MoreIntervals/compact_.con.
132 (*#* Finite intervals have a left end and a right end. *)
134 inline cic:/CoRN/ftc/MoreIntervals/left_end.con.
136 inline cic:/CoRN/ftc/MoreIntervals/right_end.con.
139 Some trivia: compact intervals are finite; proper intervals are nonvoid; an interval is nonvoid iff it contains some point.
142 inline cic:/CoRN/ftc/MoreIntervals/compact_finite.con.
144 inline cic:/CoRN/ftc/MoreIntervals/proper_nonvoid.con.
146 inline cic:/CoRN/ftc/MoreIntervals/nonvoid_point.con.
148 inline cic:/CoRN/ftc/MoreIntervals/nonvoid_char.con.
151 For practical reasons it helps to define left end and right end of compact intervals.
154 inline cic:/CoRN/ftc/MoreIntervals/Lend.con.
156 inline cic:/CoRN/ftc/MoreIntervals/Rend.con.
158 (*#* In a compact interval, the left end is always less than or equal
162 inline cic:/CoRN/ftc/MoreIntervals/Lend_leEq_Rend.con.
165 Some nice characterizations of inclusion:
168 inline cic:/CoRN/ftc/MoreIntervals/compact_included.con.
170 inline cic:/CoRN/ftc/MoreIntervals/included_interval'.con.
172 inline cic:/CoRN/ftc/MoreIntervals/included_interval.con.
175 A weirder inclusion result.
178 inline cic:/CoRN/ftc/MoreIntervals/included3_interval.con.
181 Finally, all intervals are characterized by well defined predicates.
184 inline cic:/CoRN/ftc/MoreIntervals/iprop_wd.con.
191 Implicit Arguments Lend [I].
195 Implicit Arguments Rend [I].
199 Section Compact_Constructions.
203 Section Single_Compact_Interval.
206 (*#* **Constructions with Compact Intervals
208 Several important constructions are now discussed.
210 We begin by defining the compact interval [[x,x]].
212 %\begin{convention}% Let [P:IR->CProp] be well defined, and [x:IR]
213 such that [P(x)] holds.
217 inline cic:/CoRN/ftc/MoreIntervals/P.var.
219 inline cic:/CoRN/ftc/MoreIntervals/wdP.var.
221 inline cic:/CoRN/ftc/MoreIntervals/x.var.
223 inline cic:/CoRN/ftc/MoreIntervals/Hx.var.
225 inline cic:/CoRN/ftc/MoreIntervals/compact_single.con.
228 This interval contains [x] and only (elements equal to) [x]; furthermore, for every (well-defined) [P], if $x\in P$#x∈P# then $[x,x]\subseteq P$#[x,x]⊆P#.
231 inline cic:/CoRN/ftc/MoreIntervals/compact_single_prop.con.
233 inline cic:/CoRN/ftc/MoreIntervals/compact_single_pt.con.
235 inline cic:/CoRN/ftc/MoreIntervals/compact_single_inc.con.
238 End Single_Compact_Interval.
242 The special case of intervals is worth singling out, as one of the hypothesis becomes a theorem.
245 inline cic:/CoRN/ftc/MoreIntervals/compact_single_iprop.con.
248 Now for more interesting and important results.
250 Let [I] be a proper interval and [x] be a point of [I]. Then there is
251 a proper compact interval [[a,b]] such that $x\in[a,b]\subseteq
252 I$#x∈[a,b]⊆I#.
256 Section Proper_Compact_with_One_or_Two_Points.
261 inline cic:/CoRN/ftc/MoreIntervals/cip1'.con.
263 inline cic:/CoRN/ftc/MoreIntervals/cip1''.con.
265 inline cic:/CoRN/ftc/MoreIntervals/cip1'''.con.
267 inline cic:/CoRN/ftc/MoreIntervals/cip1''''.con.
269 inline cic:/CoRN/ftc/MoreIntervals/cip2.con.
271 inline cic:/CoRN/ftc/MoreIntervals/cip2'.con.
273 inline cic:/CoRN/ftc/MoreIntervals/cip2''.con.
275 inline cic:/CoRN/ftc/MoreIntervals/cip2'''.con.
277 inline cic:/CoRN/ftc/MoreIntervals/cip3.con.
279 inline cic:/CoRN/ftc/MoreIntervals/cip3'.con.
281 inline cic:/CoRN/ftc/MoreIntervals/cip3''.con.
283 inline cic:/CoRN/ftc/MoreIntervals/cip3'''.con.
287 inline cic:/CoRN/ftc/MoreIntervals/compact_in_interval.con.
289 inline cic:/CoRN/ftc/MoreIntervals/compact_compact_in_interval.con.
291 inline cic:/CoRN/ftc/MoreIntervals/proper_compact_in_interval.con.
293 inline cic:/CoRN/ftc/MoreIntervals/proper_compact_in_interval'.con.
295 inline cic:/CoRN/ftc/MoreIntervals/included_compact_in_interval.con.
297 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval.con.
299 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval'.con.
301 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval_inc1.con.
303 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval_inc2.con.
306 If [x [=] y] then the construction yields the same interval whether we
307 use [x] or [y] in its definition. This property is required at some
308 stage, which is why we formalized this result as a functional
309 definition rather than as an existential formula.
312 inline cic:/CoRN/ftc/MoreIntervals/compact_in_interval_wd1.con.
314 inline cic:/CoRN/ftc/MoreIntervals/compact_in_interval_wd2.con.
317 We can make an analogous construction for two points.
320 inline cic:/CoRN/ftc/MoreIntervals/compact_in_interval2.con.
322 inline cic:/CoRN/ftc/MoreIntervals/compact_compact_in_interval2.con.
324 inline cic:/CoRN/ftc/MoreIntervals/proper_compact_in_interval2.con.
326 inline cic:/CoRN/ftc/MoreIntervals/proper_compact_in_interval2'.con.
328 inline cic:/CoRN/ftc/MoreIntervals/included_compact_in_interval2.con.
330 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval2x.con.
332 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval2y.con.
334 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval2x'.con.
336 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval2y'.con.
338 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval2_inc1.con.
340 inline cic:/CoRN/ftc/MoreIntervals/iprop_compact_in_interval2_inc2.con.
342 inline cic:/CoRN/ftc/MoreIntervals/compact_in_interval_x_lft.con.
344 inline cic:/CoRN/ftc/MoreIntervals/compact_in_interval_y_lft.con.
346 inline cic:/CoRN/ftc/MoreIntervals/compact_in_interval_x_rht.con.
348 inline cic:/CoRN/ftc/MoreIntervals/compact_in_interval_y_rht.con.
351 End Proper_Compact_with_One_or_Two_Points.
355 Compact intervals are exactly compact intervals(!).
358 inline cic:/CoRN/ftc/MoreIntervals/interval_compact_inc.con.
360 inline cic:/CoRN/ftc/MoreIntervals/compact_interval_inc.con.
363 A generalization of the previous results: if $[a,b]\subseteq J$#[a,b]⊆J#
364 and [J] is proper, then we can find a proper interval [[a',b']] such that
365 $[a,b]\subseteq[a',b']\subseteq J$#[a,b]⊆[a',b']⊆J#.
368 inline cic:/CoRN/ftc/MoreIntervals/compact_proper_in_interval.con.
371 End Compact_Constructions.
378 (*#* **Properties of Functions in Intervals
380 We now define notions of continuity, differentiability and so on on
381 arbitrary intervals. As expected, a function [F] has property [P] in
382 the (proper) interval [I] iff it has property [P] in every compact
383 interval included in [I]. We can formalize this in a nice way using
384 previously defined concepts.
386 %\begin{convention}% Let [n:nat] and [I:interval].
390 inline cic:/CoRN/ftc/MoreIntervals/n.var.
392 inline cic:/CoRN/ftc/MoreIntervals/I.var.
394 inline cic:/CoRN/ftc/MoreIntervals/Continuous.con.
396 inline cic:/CoRN/ftc/MoreIntervals/Derivative.con.
398 inline cic:/CoRN/ftc/MoreIntervals/Diffble.con.
400 inline cic:/CoRN/ftc/MoreIntervals/Derivative_n.con.
402 inline cic:/CoRN/ftc/MoreIntervals/Diffble_n.con.
409 Section Reflexivity_Properties.
413 In the case of compact intervals, this definitions collapse to the old ones.
416 inline cic:/CoRN/ftc/MoreIntervals/Continuous_Int.con.
418 inline cic:/CoRN/ftc/MoreIntervals/Int_Continuous.con.
420 inline cic:/CoRN/ftc/MoreIntervals/Derivative_Int.con.
422 inline cic:/CoRN/ftc/MoreIntervals/Int_Derivative.con.
424 inline cic:/CoRN/ftc/MoreIntervals/Diffble_Int.con.
426 inline cic:/CoRN/ftc/MoreIntervals/Int_Diffble.con.
429 End Reflexivity_Properties.
437 Interestingly, inclusion and equality in an interval are also characterizable in a similar way:
440 inline cic:/CoRN/ftc/MoreIntervals/included_imp_inc.con.
442 inline cic:/CoRN/ftc/MoreIntervals/included_Feq''.con.
444 inline cic:/CoRN/ftc/MoreIntervals/included_Feq'.con.
451 Hint Resolve included_interval included_interval' included3_interval
452 compact_single_inc compact_single_iprop included_compact_in_interval
453 iprop_compact_in_interval_inc1 iprop_compact_in_interval_inc2
454 included_compact_in_interval2 iprop_compact_in_interval2_inc1
455 iprop_compact_in_interval2_inc2 interval_compact_inc compact_interval_inc