ring r =0,(x,y),dp;
  poly f = 9x16-18x13y2-9x12y3+9x10y4-18x11y2+36x8y4
         +18x7y5-18x5y6+9x6y4-18x3y6-9x2y7+9y8;
  // = 9 * (x5-1y2)^2 * (x6-2x3y2-1x2y3+y4)
  factorize(f);
  // returns factors and multiplicities, 
  // first factor is a constant.
  poly g = (y4+x8)*(x2+y2);
  factorize(g);
  // The same in charcteristic 2:
  ring r =2,(x,y),dp;
  poly g = (y4+x8)*(x2+y2);
  factorize(g);
LIB "tst.lib";tst_status(1);$