P. Cohn: On the structure of the GL_2 of a ring. Publ. Math. IHES 30 (1966), 5-54. A. Hahn/O. O'Meara: The classical groups and K-theory. Springer 1989, 590p. DM 198. J. Hilgert/Karl Heinrich Hofmann: Old and new on Sl(2). Man. Math. 54 (1985), 17-52. 1589 Guenter Scheja/Uwe Storch: Lehrbuch der Algebra I. Teubner 1994, 700p. 3-519-12203-0. DM 62.