isConstant: what should this method do?
The method quantity.Discrete/isConstant does the following, according to the methods description:
% the quantity is interpreted as constant if it has no grid or % it has a grid that is only defined at one point.
However, one could also assume, that a quantity is constant, if it has the same value on every grid point of the domain. Maybe the name of the method can be changed? If needed, additionally a real isConstant method could be implemented.