In conclusion, isomer counting methods combine mathematical inge­ nuity with chemical insight and, owing to the advancement of computer hardware and software, are nowadays able to cope with almost any prob­ lem. However, since the combinatorics of organic chemistry afford an in­ finity of isomers (possibly of aleph one type) the challenge is still present to find more direct, fast and economic methods (in terms of manpower and computer time) for counting isomers.