code: protected RedBlueMerge<SP, TP, BlueFringePTAState<SP, TP>> tryMerge(BlueFringePTA<SP, TP> pta,
                                                                          BlueFringePTAState<SP, TP> qr,
                                                                          BlueFringePTAState<SP, TP> qb) {
          return pta.tryMerge(qr, qb);
      }
docs: Attempts to merge a blue state into a red state.
  
  @param pta
  the blue fringe PTA
  @param qr
  the red state (i.e., the merge target)
  @param qb
  the blue state (i.e., the merge source)
  
  @return a valid {@link RedBlueMerge} object representing a possible merge of {@code qb} into {@code qr}, or
  {@code null} if the merge is impossible