theorem Th49:
  for L be add-unital non empty addMagma for x be Element of L holds
  (mult L).(1,x) = x
proof
  let L be add-unital non empty addMagma;
  let x be Element of L;
  0+1 = 1;
  hence (mult L).(1,x) = (mult L).(0,x) + x by Def7
    .= 0_L + x by Def7
    .= x by Def4;
end;
