code: private static String getCommonSymbol(IBond bondA, IBond bondB) {
          String symbol = "";
  
          if (bondA.contains(bondB.getBegin())) {
              symbol = bondB.getBegin().getSymbol();
          } else if (bondA.contains(bondB.getEnd())) {
              symbol = bondB.getEnd().getSymbol();
          }
  
          return symbol;
      }
docs: Determines if 2 bondA1 have 1 atom in common and returns the common symbol
  
  @param  atom  first bondA1
  @param  bondB  second bondA1
  @return    the symbol of the common atom or "" if
  the 2 bonds have no common atom