2 \ 5h1 class="section"
\ 6Effective searching
\ 5/h1
\ 6
3 The fact of being able to decide, via a computable boolean function, the
4 equality between elements of a given set is an essential prerequisite for
5 effectively searching an element of that set inside a data structure. In this
6 section we shall define several boolean functions acting on lists of elements in
7 a DeqSet, and prove some of their properties.*)
9 include "basics/list.ma".
10 include "tutorial/chapter4.ma".
12 (* The first function we define is an effective version of the membership relation,
13 between an element x and a list l. Its definition is a straightforward recursion on
16 \ 5img class="anchor" src="icons/tick.png" id="memb"
\ 6let rec memb (S:
\ 5a href="cic:/matita/tutorial/chapter4/DeqSet.ind(1,0,0)"
\ 6DeqSet
\ 5/a
\ 6) (x:S) (l:
\ 5a href="cic:/matita/basics/list/list.ind(1,0,1)"
\ 6list
\ 5/a
\ 6\ 5span class="error" title="Parse error: RPAREN expected after [term] (in [arg])"
\ 6\ 5/span
\ 6 S) on l ≝
18 [ nil ⇒
\ 5a href="cic:/matita/basics/bool/bool.con(0,2,0)"
\ 6false
\ 5/a
\ 6
19 | cons a tl ⇒ (x
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 a)
\ 5a title="boolean or" href="cic:/fakeuri.def(1)"
\ 6∨
\ 5/a
\ 6 memb S x tl
20 ]
\ 5span class="error" title="Parse error: NUMBER '1' or [term] or [sym=] expected after [sym=] (in [term])"
\ 6\ 5/span
\ 6\ 5span class="error" title="No choices for ID nil"
\ 6\ 5/span
\ 6.
22 notation < "\memb x l" non associative with precedence 90 for @{'memb $x $l}.
23 interpretation "boolean membership" 'memb a l = (memb ? a l).
25 (* We can now prove several interesing properties for memb:
26 - memb_hd: x is a member of x::l
27 - memb_cons: if x is a member of l than x is a member of a::l
28 - memb_single: if x is a member of [a] then x=a
29 - memb_append: if x is a member of l1@l2 then either x is a member of l1
30 or x is a member of l2
31 - memb_append_l1: if x is a member of l1 then x is a member of l1@l2
32 - memb_append_l2: if x is a member of l2 then x is a member of l1@l2
33 - memb_exists: if x is a member of l, than l can decomposed as l1@(x::l2)
34 - not_memb_to_not_eq: if x is not a member of l and y is, then x≠y
35 - memb_map: if a is a member of l, then (f a) is a member of (map f l)
36 - memb_compose: if a is a member of l1 and b is a meber of l2 than
37 (op a b) is a member of (compose op l1 l2)
40 \ 5img class="anchor" src="icons/tick.png" id="memb_hd"
\ 6lemma memb_hd: ∀S,a,l.
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (a
\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6l)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
41 #S #a #l normalize >(
\ 5a href="cic:/matita/basics/logic/proj2.def(2)"
\ 6proj2
\ 5/a
\ 6 … (
\ 5a href="cic:/matita/tutorial/chapter4/eqb_true.fix(0,0,4)"
\ 6eqb_true
\ 5/a
\ 6 S …) (
\ 5a href="cic:/matita/basics/logic/eq.con(0,1,2)"
\ 6refl
\ 5/a
\ 6 S a)) //
44 \ 5img class="anchor" src="icons/tick.png" id="memb_cons"
\ 6lemma memb_cons: ∀S,a,b,l.
45 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6\ 5span class="error" title="Parse error: SYMBOL '.' expected after [grafite_ncommand] (in [executable])"
\ 6\ 5/span
\ 6 S a (b
\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6l)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
46 #S #a #b #l normalize cases (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b) normalize //
49 \ 5img class="anchor" src="icons/tick.png" id="memb_single"
\ 6lemma memb_single: ∀S,a,x.
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (x
\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6\ 5a title="nil" href="cic:/fakeuri.def(1)"
\ 6[
\ 5/a
\ 6\ 5a title="nil" href="cic:/fakeuri.def(1)"
\ 6]
\ 5/a
\ 6)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 → a
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 x.
50 #S #a #x normalize cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 … (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6x)) #H
51 [#_ >(\P H) // |>H normalize #abs @
\ 5a href="cic:/matita/basics/logic/False_ind.fix(0,1,1)"
\ 6False_ind
\ 5/a
\ 6 /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/logic/absurd.def(2)"
\ 6absurd
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/]
54 \ 5img class="anchor" src="icons/tick.png" id="memb_append"
\ 6lemma memb_append: ∀S,a,l1,l2.
55 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (l1
\ 5a title="append" href="cic:/fakeuri.def(1)"
\ 6@
\ 5/a
\ 6\ 5span class="error" title="Parse error: [term level 46] expected after [sym@] (in [term])"
\ 6\ 5/span
\ 6l2)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l1
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 \ 5a title="logical or" href="cic:/fakeuri.def(1)"
\ 6∨
\ 5/a
\ 6 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l2
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
56 #S #a #l1
\ 5span class="error" title="Parse error: illegal begin of statement"
\ 6\ 5/span
\ 6\ 5span class="error" title="Parse error: illegal begin of statement"
\ 6\ 5/span
\ 6 elim l1 normalize [#l2 #H %2 //]
57 #b #tl #Hind #l2 cases (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b) normalize /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/bool/orb_true_l.def(2)"
\ 6orb_true_l
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/
60 \ 5img class="anchor" src="icons/tick.png" id="memb_append_l1"
\ 6lemma memb_append_l1: ∀S,a,l1,l2.
61 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l1
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (l1
\ 5a title="append" href="cic:/fakeuri.def(1)"
\ 6@
\ 5/a
\ 6l2)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
62 #S #a #l1 elim l1 normalize
63 [normalize #le #abs @
\ 5a href="cic:/matita/basics/logic/False_ind.fix(0,1,1)"
\ 6False_ind
\ 5/a
\ 6 /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/logic/absurd.def(2)"
\ 6absurd
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/
64 |#b #tl #Hind #l2 cases (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b) normalize /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5/span
\ 6\ 5/span
\ 6/
68 \ 5img class="anchor" src="icons/tick.png" id="memb_append_l2"
\ 6lemma memb_append_l2: ∀S,a,l1,l2.
69 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l2
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (l1
\ 5a title="append" href="cic:/fakeuri.def(1)"
\ 6@
\ 5/a
\ 6l2)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
70 #S #a #l1 elim l1 normalize //
71 #b #tl #Hind #l2 cases (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b) normalize /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5/span
\ 6\ 5/span
\ 6/
74 \ 5img class="anchor" src="icons/tick.png" id="memb_exists"
\ 6lemma memb_exists: ∀S,a,l.
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6\ 5span class="error" title="Parse error: SYMBOL '.' expected after [grafite_ncommand] (in [executable])"
\ 6\ 5/span
\ 6 →
\ 5a title="exists" href="cic:/fakeuri.def(1)"
\ 6∃
\ 5/a
\ 6l1,l2
\ 5a title="exists" href="cic:/fakeuri.def(1)"
\ 6.
\ 5/a
\ 6l
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6l1
\ 5a title="append" href="cic:/fakeuri.def(1)"
\ 6@
\ 5/a
\ 6(a
\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6l2).
75 #S #a #l elim l [normalize #abs @
\ 5a href="cic:/matita/basics/logic/False_ind.fix(0,1,1)"
\ 6False_ind
\ 5/a
\ 6 /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/logic/absurd.def(2)"
\ 6absurd
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/]
76 #b #tl #Hind #H cases (
\ 5a href="cic:/matita/basics/bool/orb_true_l.def(2)"
\ 6orb_true_l
\ 5/a
\ 6 … H)
77 [#eqba @(
\ 5a href="cic:/matita/basics/logic/ex.con(0,1,2)"
\ 6ex_intro
\ 5/a
\ 6 … (
\ 5a href="cic:/matita/basics/list/list.con(0,1,1)"
\ 6nil
\ 5/a
\ 6 S)) @(
\ 5a href="cic:/matita/basics/logic/ex.con(0,1,2)"
\ 6ex_intro
\ 5/a
\ 6 … tl) >(\P eqba) //
78 |#mem_tl cases (Hind mem_tl) #l1 * #l2 #eqtl
79 @(
\ 5a href="cic:/matita/basics/logic/ex.con(0,1,2)"
\ 6ex_intro
\ 5/a
\ 6 … (b
\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6l1)) @(
\ 5a href="cic:/matita/basics/logic/ex.con(0,1,2)"
\ 6ex_intro
\ 5/a
\ 6 … l2) >eqtl //
83 \ 5img class="anchor" src="icons/tick.png" id="not_memb_to_not_eq"
\ 6lemma not_memb_to_not_eq: ∀S,a,b,l.
84 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,2,0)"
\ 6false
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S b l
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 → a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,2,0)"
\ 6false
\ 5/a
\ 6.
85 #S #a #b #l cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b)) //
86 #eqab >(\P eqab) #H >H #abs @
\ 5a href="cic:/matita/basics/logic/False_ind.fix(0,1,1)"
\ 6False_ind
\ 5/a
\ 6 /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/logic/absurd.def(2)"
\ 6absurd
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/
89 \ 5img class="anchor" src="icons/tick.png" id="memb_map"
\ 6lemma memb_map: ∀S1,S2,f,a,l.
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S1 a l
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
90 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S2 (f a) (
\ 5a href="cic:/matita/basics/list/map.fix(0,3,1)"
\ 6map
\ 5/a
\ 6 … f l)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
91 #S1 #S2 #f #a #l elim l normalize [//]
92 #x #tl #memba cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6x))
93 [#eqx >eqx >(\P eqx) >(\b (
\ 5a href="cic:/matita/basics/logic/eq.con(0,1,2)"
\ 6refl
\ 5/a
\ 6 … (f x))) normalize //
94 |#eqx >eqx cases (f a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6f x) normalize /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5/span
\ 6\ 5/span
\ 6/
98 \ 5img class="anchor" src="icons/tick.png" id="memb_compose"
\ 6lemma memb_compose: ∀S1,S2,S3,op,a1,a2,l1,l2.
99 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S1 a1 l1
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S2 a2 l2
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
100 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S3 (op a1 a2) (
\ 5a href="cic:/matita/basics/list/compose.def(2)"
\ 6compose
\ 5/a
\ 6 S1 S2 S3 op l1 l2)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
101 #S1 #S2 #S3 #op #a1 #a2 #l1 elim l1 [normalize //]
102 #x #tl #Hind #l2 #memba1 #memba2 cases (
\ 5a href="cic:/matita/basics/bool/orb_true_l.def(2)"
\ 6orb_true_l
\ 5/a
\ 6 … memba1)
103 [#eqa1 >(\P eqa1) @
\ 5a href="cic:/matita/tutorial/chapter5/memb_append_l1.def(5)"
\ 6memb_append_l1
\ 5/a
\ 6 @
\ 5a href="cic:/matita/tutorial/chapter5/memb_map.def(5)"
\ 6memb_map
\ 5/a
\ 6 //
104 |#membtl @
\ 5a href="cic:/matita/tutorial/chapter5/memb_append_l2.def(5)"
\ 6memb_append_l2
\ 5/a
\ 6 @Hind //
109 \ 5h2 class="section"
\ 6Unicity
\ 5/h2
\ 6
110 If we are interested in representing finite sets as lists, is is convenient
111 to avoid duplications of elements. The following uniqueb check this property.
114 \ 5img class="anchor" src="icons/tick.png" id="uniqueb"
\ 6let rec uniqueb (S:
\ 5a href="cic:/matita/tutorial/chapter4/DeqSet.ind(1,0,0)"
\ 6DeqSet
\ 5/a
\ 6) l on l :
\ 5a href="cic:/matita/basics/bool/bool.ind(1,0,0)"
\ 6bool
\ 5/a
\ 6 ≝
116 [ nil ⇒
\ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6
117 | cons a tl ⇒
\ 5a href="cic:/matita/basics/bool/notb.def(1)"
\ 6notb
\ 5/a
\ 6 (
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a tl)
\ 5a title="boolean and" href="cic:/fakeuri.def(1)"
\ 6∧
\ 5/a
\ 6 uniqueb S tl
120 (* unique_append l1 l2 add l1 in fornt of l2, but preserving unicity *)
122 \ 5img class="anchor" src="icons/tick.png" id="unique_append"
\ 6let rec unique_append (S:
\ 5a href="cic:/matita/tutorial/chapter4/DeqSet.ind(1,0,0)"
\ 6DeqSet
\ 5/a
\ 6) (l1,l2:
\ 5a href="cic:/matita/basics/list/list.ind(1,0,1)"
\ 6list
\ 5/a
\ 6 S) on l1 ≝
126 let r ≝ unique_append S tl l2 in
127 if
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a r then r else a
\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6r
130 \ 5img class="anchor" src="icons/tick.png" id="memb_unique_append"
\ 6lemma memb_unique_append: ∀S,a,l1,l2.
131 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S l1 l2)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l1
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 \ 5a title="logical or" href="cic:/fakeuri.def(1)"
\ 6∨
\ 5/a
\ 6 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l2
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
132 #S #a #l1 elim l1 normalize [#l2 #H %2 //]
133 #b #tl #Hind #l2 cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 … (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b)) #Hab >Hab normalize /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/bool/orb_true_l.def(2)"
\ 6orb_true_l
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/
134 cases (
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S b (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S tl l2)) normalize
135 [@Hind | >Hab normalize @Hind]
138 \ 5img class="anchor" src="icons/tick.png" id="unique_append_elim"
\ 6lemma unique_append_elim: ∀S:
\ 5a href="cic:/matita/tutorial/chapter4/DeqSet.ind(1,0,0)"
\ 6DeqSet
\ 5/a
\ 6.∀P: S → Prop.∀l1,l2.
139 (∀x.
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S x l1
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5span class="error" title="Parse error: NUMBER '1' or [term] or [sym=] expected after [sym=] (in [term])"
\ 6\ 5/span
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 → P x) → (∀x.
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S x l2
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 → P x) →
140 ∀x.
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S x (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S l1 l2)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 → P x.
141 #S #P #l1 #l2 #Hl1 #Hl2 #x #membx cases (
\ 5a href="cic:/matita/tutorial/chapter5/memb_unique_append.def(6)"
\ 6memb_unique_append
\ 5/a
\ 6\ 5span class="error" title="No choices for ID memb_unique_append"
\ 6\ 5/span
\ 6 … membx) /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5/span
\ 6\ 5/span
\ 6/
144 \ 5img class="anchor" src="icons/tick.png" id="unique_append_unique"
\ 6lemma unique_append_unique: ∀S,l1,l2.
\ 5a href="cic:/matita/tutorial/chapter5/uniqueb.fix(0,1,5)"
\ 6uniqueb
\ 5/a
\ 6 S l2
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
145 \ 5a href="cic:/matita/tutorial/chapter5/uniqueb.fix(0,1,5)"
\ 6uniqueb
\ 5/a
\ 6 S (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S l1 l2)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
146 #S #l1 elim l1 normalize // #a #tl #Hind #l2 #uniquel2
147 cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 … (
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S tl l2)))
148 #H >H normalize [@Hind //] >H normalize @Hind //
152 \ 5h2 class="section"
\ 6Sublists
\ 5/h2
\ 6
154 \ 5img class="anchor" src="icons/tick.png" id="sublist"
\ 6definition sublist ≝
155 λS,l1,l2.∀a.
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l1
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l2
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
157 \ 5img class="anchor" src="icons/tick.png" id="sublist_length"
\ 6lemma sublist_length: ∀S,l1,l2.
158 \ 5a href="cic:/matita/tutorial/chapter5/uniqueb.fix(0,1,5)"
\ 6uniqueb
\ 5/a
\ 6 S l1
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/sublist.def(5)"
\ 6sublist
\ 5/a
\ 6 S l1 l2 →
\ 5a title="norm" href="cic:/fakeuri.def(1)"
\ 6|
\ 5/a
\ 6l1
\ 5a title="norm" href="cic:/fakeuri.def(1)"
\ 6|
\ 5/a
\ 6 \ 5a title="natural 'less or equal to'" href="cic:/fakeuri.def(1)"
\ 6≤
\ 5/a
\ 6 \ 5a title="norm" href="cic:/fakeuri.def(1)"
\ 6|
\ 5/a
\ 6l2
\ 5a title="norm" href="cic:/fakeuri.def(1)"
\ 6|
\ 5/a
\ 6.
160 #a #tl #Hind #l2 #unique #sub
161 cut (
\ 5a title="exists" href="cic:/fakeuri.def(1)"
\ 6∃
\ 5/a
\ 6l3,l4
\ 5a title="exists" href="cic:/fakeuri.def(1)"
\ 6.
\ 5/a
\ 6l2
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6l3
\ 5a title="append" href="cic:/fakeuri.def(1)"
\ 6@
\ 5/a
\ 6(a
\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6\ 5a title="cons" href="cic:/fakeuri.def(1)"
\ 6:
\ 5/a
\ 6l4)) [@
\ 5a href="cic:/matita/tutorial/chapter5/memb_exists.def(5)"
\ 6memb_exists
\ 5/a
\ 6 @sub //]
162 * #l3 * #l4 #eql2 >eql2 >
\ 5a href="cic:/matita/basics/list/length_append.def(2)"
\ 6length_append
\ 5/a
\ 6 normalize
163 applyS
\ 5a href="cic:/matita/arithmetics/nat/le_S_S.def(2)"
\ 6le_S_S
\ 5/a
\ 6 <
\ 5a href="cic:/matita/basics/list/length_append.def(2)"
\ 6length_append
\ 5/a
\ 6 @Hind [@(
\ 5a href="cic:/matita/basics/bool/andb_true_r.def(4)"
\ 6andb_true_r
\ 5/a
\ 6 … unique)]
164 >eql2 in sub; #sub #x #membx
165 cases (
\ 5a href="cic:/matita/tutorial/chapter5/memb_append.def(5)"
\ 6memb_append
\ 5/a
\ 6 … (sub x (
\ 5a href="cic:/matita/basics/bool/orb_true_r2.def(3)"
\ 6orb_true_r2
\ 5/a
\ 6 … membx)))
166 [#membxl3 @
\ 5a href="cic:/matita/tutorial/chapter5/memb_append_l1.def(5)"
\ 6memb_append_l1
\ 5/a
\ 6 //
167 |#membxal4 cases (
\ 5a href="cic:/matita/basics/bool/orb_true_l.def(2)"
\ 6orb_true_l
\ 5/a
\ 6 … membxal4)
168 [#eqxa @
\ 5a href="cic:/matita/basics/logic/False_ind.fix(0,1,1)"
\ 6False_ind
\ 5/a
\ 6 lapply (
\ 5a href="cic:/matita/basics/bool/andb_true_l.def(4)"
\ 6andb_true_l
\ 5/a
\ 6 … unique)
169 <(\P eqxa) >membx normalize /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/logic/absurd.def(2)"
\ 6absurd
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/ |#membxl4 @
\ 5a href="cic:/matita/tutorial/chapter5/memb_append_l2.def(5)"
\ 6memb_append_l2
\ 5/a
\ 6 //
174 \ 5img class="anchor" src="icons/tick.png" id="sublist_unique_append_l1"
\ 6lemma sublist_unique_append_l1:
175 ∀S,l1,l2.
\ 5a href="cic:/matita/tutorial/chapter5/sublist.def(5)"
\ 6sublist
\ 5/a
\ 6 S l1 (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S l1 l2).
176 #S #l1 elim l1 normalize [#l2 #S #abs @
\ 5a href="cic:/matita/basics/logic/False_ind.fix(0,1,1)"
\ 6False_ind
\ 5/a
\ 6 /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/logic/absurd.def(2)"
\ 6absurd
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/]
178 normalize cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 … (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6x)) #eqax >eqax
179 [<(\P eqax) cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 (
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S tl l2)))
180 [#H >H normalize // | #H >H normalize >(\b (
\ 5a href="cic:/matita/basics/logic/eq.con(0,1,2)"
\ 6refl
\ 5/a
\ 6 … a)) //]
181 |cases (
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S x (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S tl l2)) normalize
182 [/
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5/span
\ 6\ 5/span
\ 6/ |>eqax normalize /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5/span
\ 6\ 5/span
\ 6/]
186 \ 5img class="anchor" src="icons/tick.png" id="sublist_unique_append_l2"
\ 6lemma sublist_unique_append_l2:
187 ∀S,l1,l2.
\ 5a href="cic:/matita/tutorial/chapter5/sublist.def(5)"
\ 6sublist
\ 5/a
\ 6 S l2 (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S l1 l2).
188 #S #l1 elim l1 [normalize //] #x #tl #Hind normalize
189 #l2 #a cases (
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S x (
\ 5a href="cic:/matita/tutorial/chapter5/unique_append.fix(0,1,5)"
\ 6unique_append
\ 5/a
\ 6 S tl l2)) normalize
190 [@Hind | cases (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6x) normalize // @Hind]
193 \ 5img class="anchor" src="icons/tick.png" id="decidable_sublist"
\ 6lemma decidable_sublist:∀S,l1,l2.
194 (
\ 5a href="cic:/matita/tutorial/chapter5/sublist.def(5)"
\ 6sublist
\ 5/a
\ 6 S l1 l2)
\ 5a title="logical or" href="cic:/fakeuri.def(1)"
\ 6∨
\ 5/a
\ 6 \ 5a title="logical not" href="cic:/fakeuri.def(1)"
\ 6¬
\ 5/a
\ 6(
\ 5a href="cic:/matita/tutorial/chapter5/sublist.def(5)"
\ 6sublist
\ 5/a
\ 6 S l1 l2).
196 [%1 #a normalize in ⊢ (%→?); #abs @
\ 5a href="cic:/matita/basics/logic/False_ind.fix(0,1,1)"
\ 6False_ind
\ 5/a
\ 6 /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/logic/absurd.def(2)"
\ 6absurd
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/
198 [cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 (
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l2)) #memba
199 [%1 whd #x #membx cases (
\ 5a href="cic:/matita/basics/bool/orb_true_l.def(2)"
\ 6orb_true_l
\ 5/a
\ 6 … membx)
200 [#eqax >(\P eqax) // |@subtl]
201 |%2 @(
\ 5a href="cic:/matita/basics/logic/not_to_not.def(3)"
\ 6not_to_not
\ 5/a
\ 6 … (
\ 5a href="cic:/matita/basics/bool/eqnot_to_noteq.def(4)"
\ 6eqnot_to_noteq
\ 5/a
\ 6 …
\ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 memba)) #H1 @H1 @
\ 5a href="cic:/matita/tutorial/chapter5/memb_hd.def(5)"
\ 6memb_hd
\ 5/a
\ 6
203 |%2 @(
\ 5a href="cic:/matita/basics/logic/not_to_not.def(3)"
\ 6not_to_not
\ 5/a
\ 6 … subtl) #H1 #x #H2 @H1 @
\ 5a href="cic:/matita/tutorial/chapter5/memb_cons.def(5)"
\ 6memb_cons
\ 5/a
\ 6 //
208 (*
\ 5h2 class="section"
\ 6Filtering
\ 5/h2
\ 6*)
210 \ 5img class="anchor" src="icons/tick.png" id="memb_filter_true"
\ 6lemma memb_filter_true: ∀S,f,a,l.
211 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (
\ 5a href="cic:/matita/basics/list/filter.def(2)"
\ 6filter
\ 5/a
\ 6 S f l)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 → f a
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
212 #S #f #a #l elim l [normalize #H @
\ 5a href="cic:/matita/basics/logic/False_ind.fix(0,1,1)"
\ 6False_ind
\ 5/a
\ 6 /
\ 5span class="autotactic"
\ 62
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/logic/absurd.def(2)"
\ 6absurd
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/]
213 #b #tl #Hind cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 (f b)) #H
214 normalize >H normalize [2:@Hind]
215 cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b)) #eqab
216 [#_ >(\P eqab) // | >eqab normalize @Hind]
219 \ 5img class="anchor" src="icons/tick.png" id="memb_filter_memb"
\ 6lemma memb_filter_memb: ∀S,f,a,l.
220 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a (
\ 5a href="cic:/matita/basics/list/filter.def(2)"
\ 6filter
\ 5/a
\ 6 S f l)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S a l
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
221 #S #f #a #l elim l [normalize //]
222 #b #tl #Hind normalize (cases (f b)) normalize
223 cases (a
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b) normalize // @Hind
226 \ 5img class="anchor" src="icons/tick.png" id="memb_filter"
\ 6lemma memb_filter: ∀S,f,l,x.
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S x (
\ 5a href="cic:/matita/basics/list/filter.def(2)"
\ 6filter
\ 5/a
\ 6 ? f l)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
227 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S x l
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 \ 5a title="logical and" href="cic:/fakeuri.def(1)"
\ 6∧
\ 5/a
\ 6 (f x
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6).
228 /
\ 5span class="autotactic"
\ 63
\ 5span class="autotrace"
\ 6 trace
\ 5a href="cic:/matita/basics/logic/And.con(0,1,2)"
\ 6conj
\ 5/a
\ 6,
\ 5a href="cic:/matita/tutorial/chapter5/memb_filter_memb.def(5)"
\ 6memb_filter_memb
\ 5/a
\ 6,
\ 5a href="cic:/matita/tutorial/chapter5/memb_filter_true.def(5)"
\ 6memb_filter_true
\ 5/a
\ 6\ 5/span
\ 6\ 5/span
\ 6/ qed.
230 \ 5img class="anchor" src="icons/tick.png" id="memb_filter_l"
\ 6lemma memb_filter_l: ∀S,f,x,l. (f x
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6) →
\ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S x l
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6 →
231 \ 5a href="cic:/matita/tutorial/chapter5/memb.fix(0,2,4)"
\ 6memb
\ 5/a
\ 6 S x (
\ 5a href="cic:/matita/basics/list/filter.def(2)"
\ 6filter
\ 5/a
\ 6 ? f l)
\ 5a title="leibnitz's equality" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6 \ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"
\ 6true
\ 5/a
\ 6.
232 #S #f #x #l #fx elim l normalize //
233 #b #tl #Hind cases (
\ 5a href="cic:/matita/basics/bool/true_or_false.def(1)"
\ 6true_or_false
\ 5/a
\ 6 (x
\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6\ 5a title="eqb" href="cic:/fakeuri.def(1)"
\ 6=
\ 5/a
\ 6b)) #eqxb
234 [<(\P eqxb) >(\b (
\ 5a href="cic:/matita/basics/logic/eq.con(0,1,2)"
\ 6refl
\ 5/a
\ 6 … x)) >fx normalize >(\b (
\ 5a href="cic:/matita/basics/logic/eq.con(0,1,2)"
\ 6refl
\ 5/a
\ 6 … x)) normalize //
235 |>eqxb cases (f b) normalize [>eqxb normalize @Hind| @Hind]
240 \ 5h2 class="section"
\ 6Exists
\ 5/h2
\ 6
243 \ 5img class="anchor" src="icons/tick.png" id="exists"
\ 6let rec exists (A:Type[0]) (p:A →
\ 5a href="cic:/matita/basics/bool/bool.ind(1,0,0)"
\ 6bool
\ 5/a
\ 6) (l:
\ 5a href="cic:/matita/basics/list/list.ind(1,0,1)"
\ 6list
\ 5/a
\ 6 A) on l :
\ 5a href="cic:/matita/basics/bool/bool.ind(1,0,0)"
\ 6bool
\ 5/a
\ 6 ≝
245 [ nil ⇒
\ 5a href="cic:/matita/basics/bool/bool.con(0,2,0)"
\ 6false
\ 5/a
\ 6
246 | cons h t ⇒
\ 5a href="cic:/matita/basics/bool/orb.def(1)"
\ 6orb
\ 5/a
\ 6 (p h) (exists A p t)