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 eq_rect_r_eq_rect_r_eq_sym': forall {T} {A B: T} F x (H: B = A), eq_rect_r F (eq_rect_r F x (eq_sym H)) H = x.