[1] M. Hall, Jr.: Projective planes and related topics. (mimeographed lectures), California Institute of Technology 1954. MR 0071036 | Zbl 0059.13901

[2] H. Karzel: Inzidenzgruppen. mimeographed lectures, University of Hamburg (prepared by I. Pieper and K. Sörensen) 1965. Zbl 0131.19101

[3] R. Sandler: Pseudo planes and pseudo ternaries. Journal of Algebra 4 (1966), 300-316. DOI 10.1016/0021-8693(66)90043-3 | MR 0199786 | Zbl 0144.19601