Proof using.
induction l; intros; simpl in *; repeat break_match; simpl in *; subst; try congruence; eauto;
break_if; congruence.
Qed.
Definition a_equiv (l1 : list (K * V)) l2 :=
forall k,
assoc l1 k = assoc l2 k.

Lemma a_equiv_refl :
forall l,
a_equiv l l.