`nm', `dn'
----------

nm(RAT)
     :: Numerator of RAT.

dn(RAT)
     :: Denominator of RAT.

RETURN
     integer or polynomial

RAT
     rational number or rational expression

   * Numerator and denominator of a given rational expression.

   * For a rational number, they return its numerator and denominator,
     respectively.  For a rational expression whose numerator and
     denominator may contain rational numbers, they do not separate
     those rational coefficients to numerators and denominators.

   * For a rational number, the denominator is always kept positive, and
     the sign is contained in the numerator.

   * Risa/Asir does not cancel the common divisors unless otherwise
     explicitly specified by the user.  Therefore, `nm()' and `dn()'
     return the numerator and the denominator as it is, respectively.

     [2] [nm(-43/8),dn(-43/8)];
     [-43,8]
     [3] dn((x*z)/(x*y));
     y*x
     [3] dn(red((x*z)/(x*y)));
     y

References
     *Note `red': red.

