Elcock, E. W.; Foster, J. M.; Gray, P. M. D.; McGregor, J. J. and A. M. Murray "Abset a Programming Language Based on Sets: Motivation and Examples"

(1971) "Machine Intelligence 6", Meltzer, Bernard and Michie, Donald (eds) Edinburgh University Press, 1971  

Languages mentioned ABSET {1970} Set-based language