ABSTRACT
This chapter defines a relation between relations, which will play the same part for them that similarity of classes plays for classes. It calls this relation “similarity of relations,” or “likeness” when it seems desirable to use a different word from that which we use for classes. We shall assume that the domain of the one relation can be correlated with the domain of the other, and the converse domain with the converse domain; but that is not enough for the sort of resemblance which we desire to have between our two relations. The space-relations in the map have “likeness” to the space-relations in the country mapped. The “relation-number” of a given relation is the class of all those relations that are similar to the given relation.
