In his Essays in the Theory of Business Cycle published in Polish in
1933, Kalecki clearly stated the principle of effective demand in mathematical form. By 1935 he outlined his theory of employment,
demolished the then-orthodox remedy for a depression-that is, wage cutting-and pinpointed the importance of investment for economic dynamics. Thus, although his training had been in Marxist economics, he succeeded in anticipating the Keynesian system, and, as Joan Robinson has pointed out, his claim to priority of publication is indisputable although he never mentioned this fact.