let literal_op = (p: unit): set(string) => 
  Set.literal(["foo", "bar", "foobar"]);

let add_op = (s: set(string)): set(string) => 
  Set.add("foobar", s);

let remove_op = (s: set(string)): set(string) => 
  Set.remove("foobar", s);

let remove_deep = (s: (set(string), nat)): set(string) => 
  Set.remove("foobar", s[0]);

let mem_op = (s: set(string)): bool => Set.mem("foobar", s);

let size_op = (s: set(string)): nat => Set.cardinal(s);