theorem
 LastLoc(I ';' J) = LastLoc I + LastLoc J
proof
 thus LastLoc(I ';' J) = card(I ';' J) - 1 by AFINSQ_1:91
      .= card I + card J - 1 - 1 by COMPOS_1:20
      .= card I - 1 + (card J - 1)
      .= LastLoc I + (card J - 1) by AFINSQ_1:91
      .= LastLoc I + LastLoc J by AFINSQ_1:91;
end;
