16 Books in the field of string theory; A series of books and written articles in the field of string theory; A series of books, written articles, handouts and worksheets in the field of string theory; Educational books featuring string theory; Educational publications, namely, educational learning cards, flash cards, activity cards, workbooks, textbooks, activity books, story books, puzzle books, printed puzzles, teacher guides, manuals, posters and educational booklets in the field of string theory; Reference books in the field of string theory