Defines the specialization of the multiplication operator * for unary-scalar-function-quantitys. It is defined for the cases where both its arguments are USFs, and also when the first is a scalar and the second is a USF.
(=> (And (Unary-Scalar-Function-Quantity ?X) (Unary-Scalar-Function-Quantity ?Y) (* ?X ?Y ?Z)) (Unary-Scalar-Function-Quantity ?Z))