Report 78-11 Erroneous Claims Concerning the Perception

Counterexamples are provided disproving two independent claims that a simple but accurate method had been found to compute classes of symmetrically equivalent atoms in a molecule. Both methods are good approximations, but are nontheless ad hoc techniques which can sometimes fail to discriminate between atoms which arc, in fact, symmetrically distinct. A recem issue of this journal carried two papers23 dealing loop, at each stage of which a new score is computed for each directly or indirectly with "inexpensive" (in the sense of low atom based upon some function of the current score of that computational effort) methods of perceiving molecular atom arid the current scores of its immediate neighbors. More precisely, each article gives a set of rules term "score" here is used rather loosely; in the case of for scoring2 or comparing3 atoms in a molecule with the claim Morgan's algorithm it is an integer while in that of Shelley that if the scores are equal, or if the comparison shows no and Munk's it is a five-element vector. The important point difference, then the atoms arc symmetrically equivalent (i.e., is that a score is an entity which is associated with an atom can be interchanged by some symmetr) operation on the and which can be compared with the scores of other atoms molecule). Though both methods are doubtless very good in such a way that a strict "greater-less-equal" relationship approximations in the sense that they almost always yield the can be defined.