reserve i,j,k for Nat;

theorem Th11:
  for K being non empty addLoopStr, a1,a2 being Element of K holds
  (diffield(K)).(a1,a2) = a1 - a2
proof
  let K be non empty addLoopStr, a1,a2 be Element of K;
  thus (diffield(K)).(a1,a2) = (the addF of K).(a1,(comp K).a2) by FINSEQOP:82
    .= a1 - a2 by VECTSP_1:def 13;
end;
