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'.
Constructs like ` op/3' refer to the predicate `op' with arity `3'.