(**
a tactic: make a transition from one status to another one or, usually,
raise a "Fail" (@see Fail) exception in case of failure
*)
(** an unfinished proof with the optional current goal *)
(**
a tactic: make a transition from one status to another one or, usually,
raise a "Fail" (@see Fail) exception in case of failure
*)
(** an unfinished proof with the optional current goal *)