first-of-two rule

What is first-of-two rule?

first-of-two rule meaning in Information Science terminology / glossary / dictionary is:

The instruction in Dewey Decimal Classification (DDC) that works dealing in equal measure with two subjects, neither used to introduce or explain the other, are given the class number appearing first in the schedules, whether the subjects are close in the list of classes or widely separated. See also: rule of three.

 

reference: ABC-CLIO