proposition: Lemma imfset_set1 x : f @` [fset x] = [fset f x].
proof: Proof. apply/fsetP => y. by apply/imfsetP/fset1P=> [[x' /fset1P-> //]| ->]; exists x; rewrite ?fset11. 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