1 “...] at the University of Chicago in 1967. They also include some material from an earlier course on abelian categories...”

2 “... at the University of Chicago; it was announced in the catalogue as "Alge­ bra 251". What made it possible...”

3 “... at the University of Chicago - not to m~ntion the auditors of my lectures at Chicago, Heidelberg, Bonn, Frankfurt...”