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
  NE-corner C = SE-corner C implies C is horizontal
proof
  assume NE-corner C = SE-corner C;
  then S-bound C = N-bound C by SPPOL_2:1;
  hence thesis by Th16;
end;
