// set must be a case-insensitive set
// set must not contain empty string
static int substringsScoreIC_optimized1(S s, Set<S> set) {
  int maxLength = lengthOfLongestString(set);
  int n = l(s);
  Set<S> seen = ciSet();
  for i to n: {
    int k = min(i+maxLength, n);
    for (int j = i+1; j <= k; j++) {
      S sub = substring(s, i, j);
      if (set.contains(sub))
        seen.add(sub);
    }
  }
  ret l(seen);
}