PLUS

(PLUS arg0 ...)


Given no argunments, returns 0. If the first argument is a
SExpressionString (or its derived class), then the function expects all the
arguments to be strings and returns their concatenation. Otherwise, acts just
like Common Lisp's '+'. 

Note there are only 2 numberic types in Intelib Lisp, SExpressionInt and
SExpressionFloat.