Vaucher, Jean G. and Rochon, Normand "PL4 - A Low Level Language with Class" pp975-979

Rosenfeld, Jack L. (1974) Rosenfeld, Jack L. (Ed.): Information Processing 74, Proceedings of IFIP Congress 74, Stockholm, Sweden, August 5-10, 1974  

Languages mentioned PL4 {1974} Experimental Simula language for list processing