
theorem Th21:
  for F being Field holds for a,b being Element of
F holds for c being Element of NonZero F holds omf(F).(a,ovf(F).(b,c)) = ovf(F)
  .(omf(F).(a,b),c)
proof
  let F be Field;
  let a,b be Element of F;
  let c be Element of NonZero F;
  reconsider revfc = revf(F).c as Element of F by XBOOLE_0:def 5;
  thus omf(F).(a,ovf(F).(b,c)) = a*(b*revfc) by Def2
    .= a*b*revfc by REALSET2:19
    .= ovf(F).(omf(F).(a,b),c) by Def2;
end;
