(∀tl1,tl2,hd1,hd2. P tl1 tl2 → P (hd1::tl1) (hd2::tl2)) →
P l1 l2.
intros (T1 T2 l1 l2 P Hl Pnil Pcons);
-generalize in match Hl; clear Hl; generalize in match l2; clear l2;
-elim l1 1 (l2 x1); [ cases l2; intros (Hl); [assumption| simplify in Hl; destruct Hl]]
+elim l1 in Hl l2 ⊢ % 1 (l2 x1); [ cases l2; intros (Hl); [assumption| simplify in Hl; destruct Hl]]
intros 3 (tl1 IH l2); cases l2; [1: simplify; intros 1 (Hl); destruct Hl]
intros 1 (Hl); apply Pcons; apply IH; simplify in Hl; destruct Hl; assumption;
qed.
lemma eq_map : ∀A,B,f,g,l. (∀x.f x = g x) → map A B f l = map A B g l.
intros (A B f g l Efg); elim l; simplify; [1: reflexivity ];
-rewrite > (Efg t); rewrite > H; reflexivity;
+rewrite > (Efg a); rewrite > H; reflexivity;
qed.
lemma le_length_filter : \forall A,l,p.length A (filter A l p) \leq length A l.
intros;elim l
[simplify;apply le_n
- |simplify;apply (bool_elim ? (p t));intro
+ |simplify;apply (bool_elim ? (p a));intro
[simplify;apply le_S_S;assumption
|simplify;apply le_S;assumption]]
qed.
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