theorem Lm49:
   for a,b being Element of A holds
   (canHom(S)).(a-b) = (canHom(S)).a - (canHom(S)).b
   proof
     let a,b be Element of A;
     thus
     (canHom(S)).(a-b) = (canHom(S)).a + (canHom(S)).(-b) by VECTSP_1:def 20
     .= (canHom(S)).a - (canHom(S)).b by RING_2:7;
   end;
