Polynomial manipulation package.
It contains support for univariate (upolynomial.*) and multivariate polynomials (polynomial.*).
Multivariate polynomial factorization uses evaluation and bivariate Hensel lifting: evaluate away
extra variables, factor the univariate specialization, then lift to bivariate factors in Zp[x]
and verify over Z. For >2 variables, trial division checks if bivariate factors divide the original.