\input zb-basic
\input zb-ioport
\iteman{io-port 70558878}
\itemau{Bratbergsengen, Kjell}
\itemti{Relational algebra operations}
\itemso{PRISMA Workshop, 24-43 (1990).}
\itemcc{}
\itemut{}
\itemli{doi:10.1007/3-540-54132-2\_48}
\end