# In booleanpolynomialring how we can find coefficient?

Let x1 ,x2,x3, v1,v2,v3 be the variable in a booleanpolynomialring. Let
F = 1+ x1*v1*v2 + x2*v1*v2 + x1*v3+ x2*x3+ v1

Now what is the coefficient of v1*v2?
In this case it will be x1+x2.
How can I find this using sagemath.
I try to use F.coefficient(v1*v2). But it not work.
Plese help.