proposition: Theorem prop_subtype : forall c c' : Prop, (c -> c') -> prop c ⊆ prop c'.
proof: Proof. intros c c' Hcc' s [[Hc' Hs] | [Hc' Hs]]. elim (Classical_Prop.classic c); intro Hc. left. split; ok. right. unfold one in *. Ksolve. right. split. now auto. ok. Qed.
imports: Morphisms ClassicalRealizability.Tactics ClassicalRealizability.BasicResults ClassicalRealizability.Subtyping