Function tl_vsw_term 

fn tl_vsw_term(
    l: i32,
    m: i32,
    lambda: i32,
    mu: i32,
    p: i32,
    q: i32,
    rows: [&Wigner3jRow; 2],
) -> Complex

Degree-p coefficient of the coupling of source (l, m) to destination (lambda, -mu) with q = p - cross. Zero unless both Wigner 3j symbols it multiplies, (l lambda p; m mu -m-mu) from rows[0] = Wigner3jRow::new(l, lambda, m, mu) and (l lambda q; 0 0 0) from rows[1] = Wigner3jRow::new(l, lambda, 0, 0), can be nonzero.

Upstream: treams.special._tl_vsw_helper.