§1 (to Ch. XIII, § 9) Rate of return over cost expressed in the notation of the calculus

IN the notation of the calculus, the rate of return over cost, called in the text r1', is defined in terms of the partial differential quotient with the opposite sign of next year's income with respect to this year's income of Individual 1. That is, by definition

and

.

Analogous formulas express the remaining r's for Individuals 1, 2... n.