Wolff, J. Focus: Use the power of targeted thinking to get more done : Use the power of targeted thinking to get more done (2.). Pearson Education UK.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Wolff, Jurgen. Focus: Use the Power of Targeted Thinking to Get More Done : Use the Power of Targeted Thinking to Get More Done. 2. Pearson Education UK.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Wolff, Jurgen. Focus: Use the Power of Targeted Thinking to Get More Done : Use the Power of Targeted Thinking to Get More Done. 2. Pearson Education UK.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.