R = QQ[x1, x2];
p =
 -x1*x2^2 +
 x1*x2^5 +
 0*x2^9 +
 0*x2^7 +
 -x2^3 +
 x2^4 +
 x2^6 +
 0*x1*x2^8 +
 -x2;