Parity, parity, parity

John Donald Black (June 6, 1883 – April 12, 1960) was an American economist. He was a professor of economics at University of Minnesota from 1918 to 1927, and then from 1927 to 1956 at Harvard University.Black was one of the authors of the Agricultural Adjustment Act.He was also president of the American Economic Association in 1955.Black died at a Boston hospital in 1960.-Wikipedia