`fctr', `sqfr'
--------------

fctr(POLY)
     :: Factorize polynomial POLY over the rationals.

sqfr(POLY)
     :: Gets a square-free factorization of polynomial POLY.

RETURN
     list

POLY
     polynomial with rational coefficients

   * Factorizes polynomial POLY over the rationals.  `fctr()' for
     irreducible factorization; `sqfr()' for square-free factorization.

   * The result is represented by a list, whose elements are a pair
     represented as

     [[num,1],[factor,multiplicity],...].

   * Products of all factor^multiplicity and num is equal to POLY.

   * The number num is determined so that (POLY/num) is an integral
     polynomial and its content (GCD of all coefficients) is 1.  (*Note
     ptozp::.)

     [0] fctr(x^10-1);
     [[1,1],[x-1,1],[x+1,1],[x^4+x^3+x^2+x+1,1],[x^4-x^3+x^2-x+1,1]]
     [1] fctr(x^3+y^3+(z/3)^3-x*y*z);
     [[1/27,1],[9*x^2+(-9*y-3*z)*x+9*y^2-3*z*y+z^2,1],[3*x+3*y+z,1]]
     [2] A=(a+b+c+d)^2;
     a^2+(2*b+2*c+2*d)*a+b^2+(2*c+2*d)*b+c^2+2*d*c+d^2
     [3] fctr(A);
     [[1,1],[a+b+c+d,2]]
     [4] A=(x+1)*(x^2-y^2)^2;
     x^5+x^4-2*y^2*x^3-2*y^2*x^2+y^4*x+y^4
     [5] sqfr(A);
     [[1,1],[x+1,1],[-x^2+y^2,2]]
     [6] fctr(A);
     [[1,1],[x+1,1],[-x-y,2],[x-y,2]]

References
     *Note `ufctrhint': ufctrhint.

