Primitive for retrieving the upper and lower bounds of (integral) Var. Lo and Hi return the minimum and maximum (respectively) of the variable's interval. If Var has not been declared before, it will be turned into an unrestricted integer variable. If Var is a real IC variable, it will be constrained to be integral. (These changes may cause propagation.) Infinite bounds are returned as floating point numbers; all others are returned as integers. If Var is a ground integer, Lo and Hi will unified with that integer. All other cases result in a type error.