reserve S for Subset of TOP-REAL 2,
  C,C1,C2 for non empty compact Subset of TOP-REAL 2,
  p,q for Point of TOP-REAL 2;

theorem
  NW-corner C = NE-corner C implies C is vertical
proof
  assume NW-corner C = NE-corner C;
  then W-bound C = E-bound C by SPPOL_2:1;
  hence thesis by Th15;
end;
