Ries, A. (1996). Focus: The future of your company depends on it. New York: HarperBusiness.
Παραπομπή Chicago StyleRies, Al. Focus: The Future of Your Company Depends On It. New York: HarperBusiness, 1996.
Παραπομπή MLARies, Al. Focus: The Future of Your Company Depends On It. New York: HarperBusiness, 1996.
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