proposition: Lemma eta_typing: Gamma ⊢ eta s H : A.
proof: Proof. eapply preservation_under_steps. rewrite <-eta_correct. all: eauto. Qed.
imports: Morphisms Setoid Undecidability.HOU(std.std) Undecidability.HOU.calculus(prelim terms syntax semantics confluence typing order normalisation)