docs: public static CompactSketch aNotB(final Sketch skA, final Sketch skB) {
      if ((skA == null) && (skB == null)) { return null; }
      final short seedHash = (skA == null) ? skB.getSeedHash() : skA.getSeedHash();
      final HeapAnotB anotb = new HeapAnotB(seedHash);
      return anotb.aNotB(skA, skB, true, null);
    }