Description: Define reciprocal on positive fractions. It means the same thing as one
divided by the argument (although we don't define full division since we
will never need it). This is a "temporary" set used in the construction
of complex numbers df-c , and is intended to be used only by the
construction. From Proposition 9-2.5 of Gleason p. 119, who uses an
asterisk to denote this unary operation. (Contributed by NM, 6-Mar-1996)(New usage is discouraged.)