signature BasicSig = sig val swap : 'a * 'b -> 'b * 'a val length : 'a list -> int exception Lookup val enter : (''a * 'b) * (''a * 'b) list -> (''a * 'b) list val remove : (''a * 'b) list -> ''a -> (''a * 'b) list val lookup : (''a * 'b) list -> ''a -> 'b val enq : (int * int -> bool) -> int -> int list -> int list val sing : 'a -> 'a list val member : ''a list -> ''a -> bool val filter : ('a -> bool) -> 'a list -> 'a list val insert : ''a -> ''a list -> ''a list end