@misc {MATHEDUC.02421168,
    author       = {Hayen, J. and Lind, D. and Opitz, R. and Schwartze, H. and Steinhoff, O. and Vollrath, H.J. and Weidig, I.},
    title        = {Gamma, mathematics for comprehensive schools, 9th form. Gamma 9. Mathematik fuer Gesamtschulen - Erweiterungskurs.},
    howpublished = {Stuttgart: Klett. 1987. 192 p. [ISBN 3-12-749320-7]},
    year         = {1987},
    msc2010      = {U23xx},
    identifier   = {1988b.04680},
}