where r 1 and r 6 are the H 2 and CO internuclear distances, respectively, which are obviously invariant with respect to the interchange of the two H atoms. The four other internuclear distances do map to other internuclear distances in an obvious way. We note that this simple expression is an example "Monomial Symmetrization", which we describe in more detail below. Also we using the six internuclear distances instead of six transformed variables here just for clarity.