This paper by Harvard University’s F. M. Scherer traces the historical antecedents of the 1982 Merger Guidelines SSNIP (small but significant and non-transitory increase in price) approach to market definition. Surveying the prior literature, it recognizes that the person believed to have proposed the approach was Morris Adelman. The author claims a second-mover slot for his testimony in a 1972 brewing merger case, the IBM case, and the Marathon-Mobil case of 1981, along with a 1980 restatement of market definition principles in his industrial organization textbook. Intermediate contributions are also surveyed.
Scherer, F.M. "On the Paternity of a Market Delineation Approach." American Antitrust Institute Working Paper 09-01, January 2009.