# How to find the coefficient of a boolean function with respect to some variable?

Suppose we have a boolen ring with variable x1,x2,x3,v1,v2 and v3.
let
f = 1+x1*x2*v1*v2 + x3*v1*v2 + v1*v3 +x1*x2*v3.
now how i find coefficient of v1*v2? in this case it will be (x1*x2 + x3).
how can i find this using sagemath. I try to use
f.coefficient(v1*v2). But it not work.

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