proposition: Lemma handleE : handle = (fun A m m' => if m is inr x then m else m').
proof: Proof. by apply funext_dep => A; apply boolp.funext => -[]. Qed.
imports: JMeq mathcomp(all_ssreflect) mathcomp(finmap) mathcomp(classical_sets) monae_lib HB(structures) hierarchy monad_lib fail_lib state_lib trace_lib monad_transformer