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.
Chicago-referens (17:e uppl.)ebrary, Inc, och 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.
MLA-referens (9:e uppl.)ebrary, Inc, och John F. Wippel. The Ultimate Why Question: Why Is There Anything at All Rather than Nothing Whatsoever? Catholic University of America Press, 2011.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.