theorem Th23:
  for X being Subset of TOP-REAL 2, p being Point of TOP-REAL 2 st
  p in X holds (proj2|X).p = p`2
proof
  let X be Subset of TOP-REAL 2,p be Point of TOP-REAL 2;
  assume p in X;
  hence (proj2|X).p = proj2.p by FUNCT_1:49
    .= p`2 by Def6;
end;
