theorem Th43:
  h1 = g1 & h2 = g2 implies h1 + h2 = g1 + g2
proof
  assume
A1: h1 = g1 & h2 = g2;
  h1 + h2 = ((the addF of G)||the carrier of H).[h1,h2] by DefA5;
  hence thesis by A1,FUNCT_1:49;
end;
