Ries, A. (1996). Focus: The future of your company depends on it. New York: HarperBusiness.
Dyfyniad Arddull ChicagoRies, Al. Focus: The Future of Your Company Depends On It. New York: HarperBusiness, 1996.
Dyfyniad MLARies, Al. Focus: The Future of Your Company Depends On It. New York: HarperBusiness, 1996.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.