DEFINE FUNCTION

        [SIC\]DEFINE FUNCTION NAME(X,Y,Z) Expression(X,Y,Z)

    Define  an  arithmetic  user  function of several variables. The maximum
    number of variables is 4. The function definition can reference  any  of
    the  known  mathematic  operators and intrinsic or program defined func-
    tions, but not previously defined user  functions  (i.e.  user  function
    definition is not recursive).