ebrary, Inc, & Wippel, J. F. (2011). The ultimate why question: Why is there anything at all rather than nothing whatsoever? Catholic University of America Press.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)ebrary, Inc, و John F. Wippel. The Ultimate Why Question: Why Is There Anything at All Rather than Nothing Whatsoever? Washington, D.C.: Catholic University of America Press, 2011.
توثيق جمعية اللغة المعاصرة MLA (الإصدار التاسع)ebrary, Inc, و John F. Wippel. The Ultimate Why Question: Why Is There Anything at All Rather than Nothing Whatsoever? Catholic University of America Press, 2011.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.