create(), that yields a new instance of the ADT; initialize(s), that prepares a newly created instance s for further operations, or resets it to some "initial state"; copy(s, t), that puts instance s in a state equivalent to that of t; clone(t), that performs s ← create(), copy(s, t), and returns s; free(s) or destroy(s), that reclaims the memory and other resources used by s.