Function build_next_c_r_mle 

pub fn build_next_c_r_mle<F>(
    r: &[F],
    c: usize,
    field_cfg: &F::Config,
) -> Result<DenseMultilinearExtension<F::Inner>, ArithErrors>
where
    F: PrimeField,
    F::Inner: Zero,

Build the shift selector MLE next_c_mle(r, *) with the first num_vars variables fixed to r.

For each b in {0,1}^{num_vars}: next_c_mle(b) = eq(r, b - c) if b >= c next_c_mle(b) = 0 if b < c

Uses the identity next_c_mle(r, b) = eq(r, b - c) for b >= c and 0 for b < c.