Some Stuff

I've been trying to work on an implementation of a structure generator algorithm due to Faulon (its a paper in this list somewhere). One problem I have difficulty with is reduction of the number of isomers generated. For example: It may be hard to read, but the idea is that the full tree of possible ways to attach {Br, Cl, F, I} to c1ccc1 is 4 * 3 * 2 * 1 (you can attach Bromine to all four of the carbons, leaving 3 places to attach chlorine, and so on). Of course c1(Br)c(Cl)cc1 is the same as c1(Cl)c(Br)cc1 [never mind that C1(Br)=C(Cl)C=C1 is not the same as C1=C(Br)C(Cl)=C1]. Or, in other words, there is a high degree of symmetry in the tree. There is a way to solve this, perhaps even described in the paper - if I could just understand them...