Using Set Expressions
A set consists of zero or more tuples. (A set that does not contain any tuples is known as an empty set.)
The complete expression of a set consists of zero or more explicitly specified tuples, framed in curly braces:
{ [ { Tuple_expression | Member_expression } [ , { Tuple_expression | Member_expression } ] ... ] }
The member expressions specified in a set expression are converted to one-member tuple expressions.