Function monomials_up_to_degree 

pub fn monomials_up_to_degree(
    n: u32,
    max_deg: usize,
    multilinear: bool,
) -> Vec<Monomial> 

Every monomial in n variables of degree 0..=max_deg. The constant 1 is always first (index 0), which the XL solver relies on to read off constant terms.