Digital Companion to C. S. Peirce
1895-6 [c.] | That Categorical and Hypothetical Propositions are one in essence, with some connected matters | CP 1.567

The logical and hemilogical relations belong to the old class of relations of reason, while relations in re are alogical. But there are a few not unimportant relations of reason which are likewise alogical. In my paper of 1867, I committed the error of identifying those relations constituted by non-relative characters with relations of equiparance, that is, with necessarily mutual relations, and the dynamical relations with relations of disquiparance, or possibly non-mutual relations. Subsequently, falling out of one error into another, I identified the two classes respectively with relations of reason and relations in re.

1901-1902 [c.] | Definitions for Baldwin's Dictionary [R] | MS [R] 1147

An equiparance is a fact about a set of objects irrespective of their order, such as being together, being alike, being unlike

1906 | The Basis of Pragmaticism | EP 2:381

…an equiparance; that is, the relation of B to A is essentially the same as that of A to B, so far as the duality of the pair is concerned. But no equiparance whatever, with the exception of the very few that are necessary, such as identity, coexistence, etc., is a logically simple relation.

1906-7 | PAP [ed.] | NEM 4:325

Which is the more primitive (or fundamental, or simple) form of relation, that of an Equiparance (i.e. a reciprocal relation), or that of a Disquiparance? I say that it is the Disquiparance, or rather, it is the Opponency, or relation of which a specialization may be a Disquiparance.