In the ring Z[x,y] , I want to add the new variable z:=xy, and show it in the polynomial p=(ex+y)2 so that p=(ex)2+2z+y2. My attempt is to define the rings and the polynomial p
S.<e>=ZZ['e'];
R.<x,y,z>=S['x, y, z'];
p=(e*x+y)^2
and to set xy=z, we define the ideal I=(xy−z)R and the quotient Q=R/I
I=(x*y-z)*R; Q=R.quo(I)
to reduce the polynomial p modulo the ideal I we use
q=Q(p)
So far, I have a problem such that sagemath outputs an error ' Can only reduce polynomials over fields.' I want to know where is the problem ??