theorem Th24:
  a * g * h = a * (g + h)
proof
  thus a * g * h = (-h) + ((-g) + a) + g + h by RLVECT_1:def 3
    .= (-h) + (-g) + a + g + h by RLVECT_1:def 3
    .= -(g + h) + a + g + h by Th16
    .= a * (g + h) by RLVECT_1:def 3;
end;
