A set is unchanged when this operation is applied to it and the empty set.
Maximum-cardinality matching was one of the intended applications of Gabow and Tarjan's linear time algorithm for doing this when the pattern of application is known ahead of time. The time of doing this can be decreased in a series of m operations including n make-set operations to n log n by a weighted heuristic of this for one type of linked list based collection of sets. By creating a new (*) start state and then using epsilon transitions to link the new start state to the old ones, one can create a non-deterministic finite state automata to prove that regular languages are closed under this operation. This is often paired with the find operation for disjoint dataypes. A set is unchanged when this operation is applied to it and the empty set. For 10 points, name this set operation that for sets A and B returns a set with all items that are inclusively in A or B and therefore contrasts with intersection.
Maximum-cardinality matching was one of the intended applications of Gabow and Tarjan's linear time algorithm for doing this when the pattern of application is known ahead of time.
union