Denert, E., R. Franck, and W. Streng, "PLAN2D - Towards a Two-Dimensional Programming Language", pp202-213

Siefkes, Dirk (Ed.) (1974) Siefkes, Dirk (Ed.) "GI - 4. Jahrestagung, Berlin, 9.-12. Oktober 1974" LNCS 26, Berlin: Springer-Verlag, 1975  

Languages mentioned PLAN2D {1976}