The returned value should have the following operations:
min: a vector, the minimum value of the support for each component.
max: a vector, the maximum value of the support for each component.
call: a predicate function, which returns TRUE if the value is in
the support, and FALSE otherwise.
sample: a function, which returns a sample from the support. Note that
the returned value is not guaranteed to be in the support of x. You may need
to call call to check.
sup(x)The object to obtain the support of.
A support object for x.