() is available since version 1.2.13.
() function creates an empty SET on the top of the stack.
A Set is a collection that cannot contain duplicate elements.
This is an implementation of java HashSet. NULL object is permitted. It makes no guarantees as to the iteration order of the set.
The SET object could not be represented on the stack. It has to be converted in a list to be displayed.
Storing GTS into sets do not guarantee uniqueness. each GTS has a hidden id. see example.