Nicola Giocoli poses an excellent question. For some perverse reason these triangles of excess burden are now known as Harberger triangles, although they surely antedate him. I doubt if Joan Robinson is guilty: she was too smart and public-minded not to recognize that they serve to trivialize excess burden by generalizing from partial to general equilibrium. I look forward to someone answering Nicola's question better than I can. Mason Gaffney