proposition: Lemma insert_insert i s' s a : insert i s' (insert i s a) = insert i s' a.
proof: Proof. by apply funext => j; rewrite /insert; case: ifPn => // /negbTE ->. Qed.
imports: mathcomp(all_ssreflect) imonae_lib HB(structures) ihierarchy imonad_lib ifail_lib istate_lib itrace_lib imonad_transformer