Arithmetic on DATE type

Are there any nice functions that operate on DATE type variables? I'd like to be able to for example add one day to a certain date. Adding " to_date('24','HH24') " doesn't work as " + " doesn't accept date type operands. Do I have to convert it to a string and manipulate it the hard way? Are there any PD librarys around on the net? Thanks in advance,
Hans Lindberg
Gullspaangs Kraft AB Karlstad
Tel: 031-183151 EMail d7hansl_at_dtek.chalmers.se

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