In reply to kernalmode1:
There is no restriction on system functions as long as they meed the requirements of section 18.5.12 Functions in Constraints. When you get unsupported messages, it means the tool recognizes the construct but has not implemented it you.
One thing that is not clear in the LRM, is whether $pow(x,y) can be treated the same as an operator like x**y and not divide the solution space.