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tion, Collaboration, Licensing, and Public Policy," in Readings in the Management of Innovation, Michael L. Tushman and William L. Moore, eds., Ballinger Publishing Company, Cambridge, Mass., pp. 621-647; and Levin, Richard et al., 1987, "Appropriating the Returns from Industrial Research and Development," Brookings Papers on Economic Activity, No. 3, pp. 783-831.