We have tried to keep the predicate descriptions clear and concise. First the predicate name is printed in bold face, followed by the arguments in italics. Arguments are preceded by a `+', `-' or `?' sign. `+' indicates the argument is input to the predicate, `-' denotes output and `?' denotes `either input or output'.2.1 Constructs like `op3' refer to the predicate `op' with arity `3'.