(* classical_left  transforms |- A \/ B into ~B |- A *)
(* classical_right transforms |- A \/ B into ~A |- B *)

Ltac classical_right := match goal with
|- ?X \/ _ => (elim (classic X);intro;[left;trivial|right])
end.Ltac classical_left := match goal with
|- _ \/ ?X => (elim (classic X);intro;[right;trivial|left])
end.

Lemma eq_rect_eq : forall (U:Type) (p:U) (Q:U -> Type) (x:Q p) (h:p = p), x = eq_rect p Q x p h.