In the language Lisp, each of the four basic arithmetic operators appears before an arbitrary number of operands, which are separated by spaces. The resulting expression is enclosed in parentheses. The operations behave as follows. . +ab) returns the sum of all operands, and (+) returns 0. (-a b c (* a b c a b c ) returns a-b-c-... and (-a) returns-a. The minus operator must have at least one operand.