Function eq_ind 

pub fn eq_ind<F: FieldOps>(x: &[F], y: &[F]) -> F

Evaluates the equality indicator multilinear at a pair of points.

This is the 2n-variate multilinear

eq(X_0, ..., X_{n-1}, Y_0, ..., Y_{n-1}) = prod_i X_i * Y_i + (1 - X_i) * (1 - Y_i)