Burstall, R. M. and Popplestone, R. J. "POP-2 Reference Manual"

Dale et al (1968) "Machine Intelligence 2", Dale, Ella and Michie, Donald (Eds) Oliver and Boyd, Edinburgh 1968. Proceedings of the Second Annual Machine Intelligence Workshop, University of Edinburgh, September 1966.  

Languages mentioned POP-2 {1967} The first true functional language