SHOWSET: Show the contents of a string variable containing a set of
positive integers in standard set notation.

syntax: SHOWSET(x)

Where x refers to the letter variables $A...$Z. If the letter variable contains a set of positive integer then the contents of the set contained in that variable will be shown in standard set notation: { 1, 2, 3 ...} If the set is a null set then it will be displayed as: { null }, otherwise if the letter variable does not contain a set then a *** Not A Set *** message will be displayed notifying the user that the variable does not contain a set.