Returns a Boolean value that indicates whether a given object is present in the set.
- iOS 2.0+
- macOS 10.0+
- tvOS 9.0+
- watchOS 2.0+
An object to look for in the set.
an is present in the set, otherwise
Each element of the set is checked for equality with
an until a match is found or the end of the set is reached. Objects are considered equal if