Demian by Hermann Hesse
http://books.google.com/books/about/Demian.html?id=WB3wKoZRE3EC
A perennial story of identity formation written by Hermann Hesse, this classic offers another perspective on Borges' The Approach to Al-Mu'tasim, as discussed in the analysis of that story.
The Last Temptation of Christ by Nikos Kazantzakis
http://books.google.com/books/about/The_Last_Temptation_of_Christ.html?id=KKscoUF0OJsC
A novelization of the Passion of the Christ, as reimagined by Kazantzakis. He humanizes Christ in an unorthodox manner, demonstrating the result of making a messiah appear more human than symbolic. A useful reference for the themes and questions discussed in The Approach to Al-Mu'tasim.
The Newton/Leibniz Conflict in Context
http://www.math.rutgers.edu/courses/436/Honors02/newton.html
A detailed summary of the controversy as to whether Newton, Leibniz, or both discovered the mathematical principles of calculus. This real-life example sheds new light on the themes illustrated by Borges' Pierre Menard, Author of the Quixote.