theorem
  rng R misses dom R implies iter(R,2) = {}
proof
  assume
A1: rng R misses dom R;
  thus iter(R,2) = iter(R,1+1)
    .= iter(R,1)*R by Th70
    .= R*R by Th69
    .= {} by A1,RELAT_1:44;
end;
