code: public static <L1, L2, I> OneSEVPA<Pair<L1, L2>, I> xor(final OneSEVPA<L1, I> sevpa1,
                                                              final OneSEVPA<L2, I> sevpa2,
                                                              final VPDAlphabet<I> alphabet) {
          return combine(sevpa1, sevpa2, alphabet, AcceptanceCombiner.XOR);
      }
docs: Calculates the exclusive-or ("xor") of two SEVPA, and stores the result in a given mutable SEVPA.
  
  @param sevpa1
  the first SEVPA
  @param sevpa2
  the second SEVPA
  @param alphabet
  the input alphabet
  
  @return a new SEVPA representing the conjunction of the specified SEVPA