else {
final DirectedBinaryDomainCombination dc = new DirectedBinaryDomainCombination( n_terminal, c_terminal );
DDC_POOL.put( code, dc );
else {
final DirectedBinaryDomainCombination dc = new DirectedBinaryDomainCombination( n_terminal, c_terminal );
DDC_POOL.put( code, dc );