Univ_map.Multi
list-accumulating keys with a default value of the empty list
module Key : sig ... end
val set : t -> key:'a Key.t -> data:'a Base.list -> t
val find : t -> 'a Key.t -> 'a Base.list
val add : t -> key:'a Key.t -> data:'a -> t
val change : t -> 'a Key.t -> f:('a Base.list -> 'a Base.list) -> t