Pioneers of reciprocal-demand analysis aspired to “climb the rigging of geometry and spy out the heavens” of international trade theory. Accordingly, they deployed offer-curve geometry to derive key theorems on the gains from trade, the efficiency of free-trade equilibrium, the effects of...

In his celebrated 1945 essay on international trade under variable returns in a simple model the noted Dutch economist Jan Tinbergen presented his version of what Robert Baldwin calls “the sacred diagram of the international trade economist.”