creates a set structure with values x1,x2,...,xn.

creates a new set structure containing all the elements of the given collection or all the elements returned by the given iterator.

creates a new, initially empty set structure.

creates a new set structure, initially empty but capable of holding up to n elements.

checks whether the set S is empty.

https://en.wikipedia.org/wiki/Set_(abstract_data_type)#Operations.