INSERT

input: C (a collection), V (a value).
output: C'.
preconditions: V is of a type suitable for collection elements.
postconditions: C' = C with value V added. Storage is allocated as needed. If V already occurs in C, C' contains an additional copy of V.

DELETE

input: C (a collection), V (a value).
output: C'.
preconditions: V is of a type suitable for collection elements.
postconditions: C' = C with value V removed.
If V does not occur in C, the operation does nothing. If there are several copies of V in C, just one is deleted. If possible, the storage associated with the deleted occurrence of V is returned to the global pool.