code: private IBond findBond(IAtom beg1, IAtom beg2, IAtom end) {
          IBond bond = container.getBond(beg1, end);
          if (bond != null)
              return bond;
          return container.getBond(beg2, end);
      }
docs: Find a bond between two possible atoms. For example beg1 - end or
  beg2 - end.
  @param beg1 begin 1
  @param beg2 begin 2
  @param end end
  @return the bond (or null if none)