destruct (Varseq_dec p p0).
left;f_equal;assumption.
right;injection;intro;contradiction.
left;reflexivity.
Qed.

(* Specifications: *)
Lemma Excluded_Middle : forall Γ A, Γ ⊢ A∨¬A.
intros;apply BotC;mp;[is_ass|apply OrI2;apply ImpI;mp;[is_ass|apply OrI1;is_ass]].