Primitive for retrieving the upper and lower bounds of Var. Lo and Hi return the minimum and maximum (respectively) of the variable's interval in floating point format (regardless of the variable's type). If Var has not been declared before, it will be turned into an unrestricted real variable. If Var is a ground number, Lo and Hi will give appropriate bounds based on the type and value of Var: exact bounds for floats, bounded reals and exactly representable integers, and best safe approximations for large integers and rationals.