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
  LSeg(NW-corner X, N-min X)/\X = {N-min X} & LSeg(N-max X, NE-corner X)
  /\X = {N-max X}
proof
  now
    let x be object;
A1: N-min X in LSeg(NW-corner X, N-min X) by RLTOPSP1:68;
    hereby
      N-min X in N-most X by Th42;
      then NW-corner X in LSeg(NW-corner X, NE-corner X) & N-min X in LSeg(
      NW-corner X, NE-corner X) by RLTOPSP1:68,XBOOLE_0:def 4;
      then
A2:   LSeg
(NW-corner X, N-min X) c= LSeg(NW-corner X, NE-corner X) by TOPREAL1:6;
      assume
A3:   x in LSeg(NW-corner X, N-min X)/\X;
      then
A4:   x in LSeg(NW-corner X, N-min X) by XBOOLE_0:def 4;
      reconsider p = x as Point of TOP-REAL 2 by A3;
      x in X by A3,XBOOLE_0:def 4;
      then p in N-most X by A4,A2,XBOOLE_0:def 4;
      then
A5:   (N-min X)`1 <= p`1 by Th39;
      (NW-corner X)`1 <= (N-min X)`1 by Th38;
      then p`1 <= (N-min X)`1 by A4,TOPREAL1:3;
      then
A6:   p`1 = (N-min X)`1 by A5,XXREAL_0:1;
      (NW-corner X)`2 = (N-min X)`2 by Th37;
      then
A7:   p`2 = (N-min X)`2 by A4,GOBOARD7:6;
      p = |[p`1, p`2]| by EUCLID:53;
      hence x = N-min X by A7,A6,EUCLID:53;
    end;
    N-min X in N-most X by Th42;
    then
A8: N-min X in X by XBOOLE_0:def 4;
    assume x = N-min X;
    hence x in LSeg(NW-corner X, N-min X)/\X by A8,A1,XBOOLE_0:def 4;
  end;
  hence LSeg(NW-corner X, N-min X)/\X = {N-min X} by TARSKI:def 1;
  now
    let x be object;
A9: N-max X in LSeg(N-max X, NE-corner X) by RLTOPSP1:68;
    hereby
      N-max X in N-most X by Th42;
      then NE-corner X in LSeg(NW-corner X, NE-corner X) & N-max X in LSeg(
      NW-corner X, NE-corner X) by RLTOPSP1:68,XBOOLE_0:def 4;
      then
A10:  LSeg
(N-max X, NE-corner X) c= LSeg(NW-corner X, NE-corner X) by TOPREAL1:6;
      assume
A11:  x in LSeg(N-max X, NE-corner X)/\X;
      then
A12:  x in LSeg(N-max X, NE-corner X) by XBOOLE_0:def 4;
      reconsider p = x as Point of TOP-REAL 2 by A11;
      x in X by A11,XBOOLE_0:def 4;
      then p in N-most X by A12,A10,XBOOLE_0:def 4;
      then
A13:  p`1 <= (N-max X)`1 by Th39;
      (N-max X)`1 <= (NE-corner X)`1 by Th38;
      then (N-max X)`1 <= p`1 by A12,TOPREAL1:3;
      then
A14:  p`1 = (N-max X)`1 by A13,XXREAL_0:1;
      (NE-corner X)`2 = (N-max X)`2 by Th37;
      then
A15:  p`2 = (N-max X)`2 by A12,GOBOARD7:6;
      p = |[p`1, p`2]| by EUCLID:53;
      hence x = N-max X by A15,A14,EUCLID:53;
    end;
    N-max X in N-most X by Th42;
    then
A16: N-max X in X by XBOOLE_0:def 4;
    assume x = N-max X;
    hence x in LSeg(N-max X, NE-corner X)/\X by A16,A9,XBOOLE_0:def 4;
  end;
  hence thesis by TARSKI:def 1;
end;
