induction ls; intros; simpl in *.
discriminate.
destruct a.
case_eq (eqb y b0); intros.
rewrite H0 in H.
case_eq (eqb x1 a); intros.
rewrite H1 in H.
simpl in *.
eapply IHls in H.
intuition.
rewrite H1 in H.
simpl in *.
inversion H; clear H; subst.
rewrite eqb_leibniz in H0.
subst.
intuition.
subst.
rewrite eqb_refl in H1.
discriminate.
rewrite H0 in H.
simpl in *.
eapply IHls in H.
intuition.
Qed.

Theorem findCollision_correct :
forall (A B : Set) eqd1 eqd2 (ls : list (A * B)) (x1 x2 : A) y,
findCollision eqd1 eqd2 ls =
Some (x1, x2, y) ->
x1 <> x2 /\
In (x1, y) ls /\
In (x2, y) ls.