SUM number1 number2
(SUM number1 number2 number3 . . .)
SUM outputs the result of adding its inputs. SUM excepts exactly two inputs, but will accept more if it and its inputs are enclosed within parentheses.
SUM is equivalent to the infix operator +.
? SUM 3 6
? SUM 3.2 6.4
? (SUM 3.2 6.4 1)