docs: public BitSet getInputSet(ValueNumber output) {
          BitSet outputSet = outputToInputMap.get(output);
          if (outputSet == null) {
              if (DEBUG) {
                  System.out.println("Create new input set for " + output.getNumber());
              }
              outputSet = new BitSet();
              outputToInputMap.put(output, outputSet);
          }
          return outputSet;
      }