Ltac solve_JMeq_sumtype H :=
  match type of H with
  | JMeq ?x ?y =>
    destruct x; destruct y;
     [apply JMeq_sumtype_ll in H; auto
     |apply JMeq_sumtype_lr in H; auto; inversion H
     |apply JMeq_sumtype_rl in H; auto; inversion H
     |apply JMeq_sumtype_rr in H; auto]
  end.

Lemma JMeq_pair: forall (A: Type) (B: Type) (C: Type) (D: Type) (a: A) (b: B) (c: C) (d: D), JMeq a b -> JMeq c d -> JMeq (a, c) (b, d).