
theorem Th15:
  for F being Field holds for a being Element of F holds osf(F).(a,0.F) = a
proof
  let F be Field;
  let a be Element of F;
  thus osf(F).(a,0.F) = (the addF of F).(a,(comp F).0.F) by Def1
    .= (the addF of F).(a,-0.F) by VECTSP_1:def 13
    .= a+0.F by RLVECT_1:12
    .= a by REALSET2:2;
end;
