The pseudo-operations "cand" and "cor" provide "conditional" and/or
operations.  They do not evaluate their right argument unless they
have to to determine the result.  In particular

                a cand b

is equivalent to

                if
                    a ==> b
                #   else ==> False
                fi

and

                a cor b

is equivalent to

                if
                    a ==> True
                #   else ==> b
                fi

where True and False are selected from the built-in Boolean type (and
implicitly applied to empty argument lists).