Reinfelds, Juris; Vandoni, Carlo E.; "Sigma 76" pp963-968

Information Processing 77 (Proc. (1977) Information Processing 77 (Proc. IFIP Congress 77, Toronto, August 8-12, 1977), Vol. 7, Elsevier North-Holland, Inc., New York, 1977  

Languages mentioned SIGMA 76 {1976} Improved version of SIGMA