val if_: start: tactic -> continuation: tactic -> fail: tactic -> tactic
val seq: tactics: tactic list -> tactic (** "folding" of then_ *)
val repeat_tactic: tactic: tactic -> tactic
val if_: start: tactic -> continuation: tactic -> fail: tactic -> tactic
val seq: tactics: tactic list -> tactic (** "folding" of then_ *)
val repeat_tactic: tactic: tactic -> tactic