Beyond and Back - The Story of XX Twenty fourth letter of the alphabet. A cross on its side. A variable common to algebraic equations and higher mathematics. A prefix of the English language. A Motion Picture Association of America rating for adults only movies. A type of chromosome. An axis in a three dimensional system. A viral encephalitis. A measure of the height of a printed letter. An unknown quantity. An American rock 'n' roll band. Edited by f Stop Fitzgerald Text by Chris