In a works cited page in MLA format, when citing a book part of the citation is, for example,
Stewart, James. Calculus: Early Transcendentals. [EDITION] ed. Belmont: Brooks/Cole, 2009. Print.
This calculus textbook is the AP edition of the Sixth edition of the textbook. Should [EDITION] be written as "AP ed. Sixth ed."?
The Library of Congress has another edition and cite it as: "7th ed., alternate ed.".
Without knowing how the main title page (as a librarian that's the most important source for cataloging a book) or other parts of the book look like, I'd say it is the 6th ed. of the AP ed.: "6th. ed, AP ed.".
I recommend going to your next academic library and asking a librarian/cataloger on-site.
