Primitive for retrieving the (finite, integral) upper and lower bounds of 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 integer variable. If Var is a real IC variable, it will be constrained to be integral. If any bound is infinite, it has a default bound imposed to make it finite (-10000000 for lower bounds, 10000000 for upper bounds). (These changes may cause propagation.) Bounds are always 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.