code: private boolean feasible(IQueryBond qbond, IBond bond) {
          if (bond == null || !qbond.matches(bond))
              return false;
          store(currBondIdx() + 1, null);
          return true;
      }
docs: Determine if a bond from the molecule exists and if it is matched
  by the query bond. If the match is feasible the current query bond index
  is increment and stored on the stack.
  
  @param qbond bond from the query
  @param bond bond from the molecule
  @return the match was feasible and the state was stored