fact: Example chain3_prop : forall c₁ c₂ c₃ : Prop, forall e, (c₁ -> c₂ -> c₃) -> Id↓e ⊩ prop c₁ → prop c₂ → prop c₃.
imports: Morphisms ClassicalRealizability.Tactics ClassicalRealizability.BasicResults ClassicalRealizability.Subtyping