static long checkSuffixTree(SuffixTree tree) {
  long numChecks = 0;
  for ping (S pattern : allSubstringsWithoutEmpty(tree.fullText)) {
    L<Int> correct = indicesOf(tree.fullText, pattern);
    L<Int> out = sorted(tree.indicesOf(pattern));
    assertEquals(pattern, correct, out);
    ++numChecks;
  }
  ret numChecks;
}