December, 8 is the Memory day of academician Andrei Ershov. To this date we publish the speech of Cornelis H.A. Koster, University of Nijmegen, The Netherlands, at the memorial session of the Sixth International Andrei Ershov Memorial Conference PERSPECTIVES OF SYSTEM INFORMATICS that was held to honour the 75th Anniversary of academician Andrei Ershov (1931-1988).