-lemma memb_exists: ∀S,a,l.memb S a l = true\ 5a href="cic:/matita/basics/bool/bool.con(0,1,0)"\ 6\ 5/a\ 6 → ∃l1,l2.l=l1@(a::l2).
-#S #a #l elim l [normalize #abs @False_ind /\ 5span class="autotactic"\ 62\ 5span class="autotrace"\ 6 trace absurd\ 5/span\ 6\ 5/span\ 6/]
-#b #tl #Hind #H cases (orb_true_l … H)
- [#eqba @(ex_intro … (nil S)) @(ex_intro … tl) >(\P eqba) //
+lemma 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.l\ 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:l2).
+#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/]
+#b #tl #Hind #H cases (\ 5a href="cic:/matita/basics/bool/orb_true_l.def(2)"\ 6orb_true_l\ 5/a\ 6 … H)
+ [#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) //