Enact a new rule entitled “Functions”:

If two Atoms’ Essences have exactly one Essential Letter in common, then there exists a Function between the dissimilar Essential Letters of those Atoms’ Essences. (The Function may be considered a bijection because it is symmetric.) Such a Function is said to go through the Domains of the corresponding Atoms. If two different (though not necessarily disjoint) pairs of Atoms both have Functions between the same Essential Letters, those pairs and their Functions are said to be homomorphic. If both Functions additionally go through the same Domains, they are said to be isomorphic.