svoid test_LCSortedPairIndex() {
  long pairs[] = toLongArray(shuffled(lmap toLong(ll(500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500))));
  printStruct(pairs);
  LCSortedPairIndex index = new(pairs);
  printStruct(index.index);
  for i over pairs:
    assertEqualsVerbose(i, index.get(pairs[i]));
  assertEquals(-1, index.get(777));
}