Function check_index_lengths 

pub fn check_index_lengths<Ix1, Ix2, Source, A, B, C>(
    ix1: &Ref<Ix1>,
    ix2: &Ref<Ix2>,
    source: &Ref<Source>,
) -> Result<(), MechError>
where
    Ix1: AsRef<[A]>,
    Ix2: AsRef<[B]>,
    Source: AsRef<[C]>,