proposition: Lemma demo_inject_and_injects : forall a b c, (a,b,c) = (1,2,3) -> b = 2.
proof: Proof. Proof using. introv EQ. dup 5. injection EQ. demo. inject EQ. demo. inject EQ as EQ1 EQ2 EQ3. demo. injects EQ. demo. symmetry in EQ. injects EQ. demo. Qed.
imports: TLC(LibTactics) Coq.micromega.Lia