reserve r, s, t, g for Real,

          r3, r1, r2, q3, p3 for Real;
reserve T for TopStruct,
  f for RealMap of T;
reserve p for Point of TOP-REAL 2,
  P for Subset of TOP-REAL 2,
  Z for non empty Subset of TOP-REAL 2,
  X for non empty compact Subset of TOP-REAL 2;

theorem
  (NW-corner P)`2 = (NE-corner P)`2
proof
  thus (NW-corner P)`2 = N-bound P by EUCLID:52
    .= (NE-corner P)`2 by EUCLID:52;
end;
