proposition: Lemma test_orb (P Q R : bool) : P \/ Q -> R.
proof: Proof. move=> p_q. case: p_q. Abort. About iffP. About idP. Lemma eqnP {n m : nat} : reflect (n = m) (eqn n m). Proof. apply: (iffP idP). elim: n m => [|n IH] m; case: m => // m Hm. by rewrite (IH m Hm). move=> def_n; rewrite {}def_n. Undo. move=> ->. by elim: m. Qed.
imports: mathcomp(all_ssreflect)