Morrison, interview with author, May 27, 2008.

Andrew Strominger (Harvard University), February 7, 2007.

Chris Beasley, Jonathan Heckman, and Cumrun Vafa, “GUTs and Exceptional Branes in F-Theory — I,” November 18, 2008, ; Chris Beasley, Jonathan Heckman, and Cumrun Vafa, “GUTs and Exceptional Branes in F-Theory — II: Experimental Predictions,” June 12, 2008, ; Ron Donagi and Martijn Wijnholt, “Model Building with F-Theory,” March 3, 2008, ; and Ron Donagi and Martijn Wijnholt, “Breaking GUT Groups in F-Theory,” August 17, 2008, .