`red'
-----

red(RAT)
     :: Reduced form of RAT by canceling common divisors.

RETURN
     rational expression

RAT
     rational expression

   * Asir automatically performs cancellation of common divisors of
     rational numb ers.  But, without an explicit command, it does not
     cancel common polynomial divisors of rational expressions.
     (Reduction of rational expressions to a common denominator will be
     always done.)  Use command red() to perform this cancellation.

   * Cancel the common divisors of the numerator and the denominator of
     a rational expression RAT by computing their GCD.

   * The denominator polynomial of the result is an integral polynomial
     which has no common divisors in its coefficients, while the
     numerator may have rational coefficients.

   * Since GCD computation is a very hard operation, it is desirable to
     detect and remove by any means common divisors as far as possible.
     Furthermore, a call to this function after swelling of the
     denominator and the numerator shall usually take a very long time.
     Therefore, often, to some extent, reduction of common divisors is
     inevitable for operations of rational expressions.

     [0] (x^3-1)/(x-1);
     (x^3-1)/(x-1)
     [1] red((x^3-1)/(x-1));
     x^2+x+1
     [2] red((x^3+y^3+z^3-3*x*y*z)/(x+y+z));
     x^2+(-y-z)*x+y^2-z*y+z^2
     [3] red((3*x*y)/(12*x^2+21*y^3*x));
     (y)/(4*x+7*y^3)
     [4] red((3/4*x^2+5/6*x)/(2*y*x+4/3*x));
     (9/8*x+5/4)/(3*y+2)

References
     *Note `nm dn': nm dn, *Note `gcd gcdz': gcd gcdz, *Note `ptozp':
     ptozp.

