There remains the further extension to what may be called “multiplicate proportion” (duplicate, triplicate, … n · plicate). This may be regarded as a limiting case of compound proportion, being a relation between variable quantities P, X of two different kinds such that measures p, x of these variables are in the proportional relation p α xn . (The definition can, of course, be expressed—like the definitions of direct and inverse proportion—in terms of ratios of any two quantities of the one kind and the two corresponding quantities of the other kind.)