interval1 and interval2 represent intervals (ranges)
constant represents a constant or constant expression
* represents the multiplication (function) on reals.
The expression function1*function2 stands for
the function composed of the multiplication function and the two
functions function1 and function2.
* can be used for interval arithmetic on intervals
(ranges). * will evaluate to an interval that safely
encompasses all images of the multiplication function with arguments varying
in the given intervals. Any combination of intervals with intervals
or constants (resp. constant expressions) is supported. However, it is
not possible to represent families of functions using an interval as
one argument and a function (varying in the free variable) as the