one solution:
add two fids as usual with the add command in procno3 having defined
with the edc2 command the two original fids in procno 1 and 2 and
having set their datmod parameter to raw.
issue the command genfid in procno3. This transforms the calculated
sum into a "real" fid, which can the be added to any other fid by the
procedure above.
stb