Function is_subset

crates/kernel/src/level.rs:535–547

(xs: &[u64], ys: &[u64])

        yi += 1;
      },
      std::cmp::Ordering::Greater => {
        yi += 1;
      },
    }
  }
  result
}

fn is_subset(xs: &[u64], ys: &[u64]) -> bool {
  let mut yi = 0;
  for &x in xs {
    while yi < ys.len() && ys[yi] < x {
      yi += 1;
    }
    if yi >= ys.len() || ys[yi] != x {
      return false;