fact: Definition output : [the functor of Output.acto L \o M] ~~> M := fun A m => let: (x, w') := m.2 in (x, m.1 ++ w').
imports: mathcomp(all_ssreflect) imonae_lib HB(structures) ihierarchy imonad_lib ifail_lib istate_lib itrace_lib imonad_transformer