module Useful:sig..end
val bool_of_opt : 'a option -> boolmodule StrMap:Map.Swith type key = string
module StrSet:Set.Swith type elt = string
module IntMap:Map.Swith type key = int
module IntSet:Set.Swith type elt = int
type'afprintf =Format.formatter -> 'a -> unit
module type ORD_PRT =sig..end