module type S =sig..end
Ephemeron.K1.Make and Ephemeron.K2.Make.
    These hash tables are weak in the keys. If all the keys of a binding are
    alive the binding is kept, but if one of the keys of the binding
    is dead then the binding is removed.mem h k is true, a subsequent
      find h k may raise Not_found because the garbage collector
      can run between the two.
      Moreover, the table shouldn't be modified during a call to iter.
      Use filter_map_inplace in this case.
include Hashtbl.S
val clean : 'a t -> unitval stats_alive : 'a t -> Hashtbl.statisticsHashtbl.SeededS.stats but only count the alive bindings