F. Cohrs, _Die evang. Katechismusversuche vor L.'s Enchiridion_
(especially I, 1 ff. and IV, 229 ff.), Arts. _Katechismen L.'s and
Katechismusunterricht_ in _Realencyk._, X, 130 ff., and XXIII, 743
ff., and _Introd. to Betbuchlein_ in _Weimar Ed._, X; O. Albrecht,
_Vorbemerkungen zu den beiden Katechismen von 1529_, in _Weimar Ed._,
XXX', 426 ff. (Further literature cited by all the above.) See also
Gecken, _Bilderkatechismus d. XV Jh_. and von Zezschwitz, _System d.
Katechetik_ (especially II, i).