5 val is_empty: 'a1 set -> bool
7 val mem : 'a1 -> 'a1 set -> bool
9 val add : 'a1 -> 'a1 set -> 'a1 set
11 val remove: 'a1 -> 'a1 set -> 'a1 set
13 val cardinal: 'a1 set -> int
15 val fold: ('a1 -> 'a -> 'a) -> 'a1 set -> 'a -> 'a
17 val iter: ('a1 -> unit) -> 'a1 set -> unit
19 val equal : 'a1 set -> 'a1 set -> bool
21 val diff : 'a1 set -> 'a1 set -> 'a1 set
23 val singleton : 'a1 -> 'a1 set
25 val subset : 'a1 set -> 'a1 set -> bool
27 val union : 'a1 set -> 'a1 set -> 'a1 set