reserve r,lambda for Real,
  i,j,n for Nat;
reserve p,p1,p2,q1,q2 for Point of TOP-REAL 2,
  P, P1 for Subset of TOP-REAL 2;
reserve T for TopSpace;

theorem Th18:
  LSeg(|[0,1]|,|[1,1]|) /\ LSeg(|[1,0]|,|[1,1]|) = {|[1,1]|}
proof
  for a being object holds a in LSeg(|[0,1]|,|[1,1]|) /\ LSeg(|[1,0]|,|[1,1]|
  ) iff a = |[1,1]|
  proof
    let a be object;
    thus a in LSeg(|[0,1]|,|[1,1]|) /\ LSeg(|[1,0]|,|[1,1]|) implies a = |[1,1
    ]|
    proof
      assume
A1:   a in LSeg(|[0,1]|,|[1,1]|) /\ LSeg(|[1,0]|,|[1,1]|);
      then a in { p : p`1 <= 1 & p`1 >= 0 & p`2 = 1} by Th13,XBOOLE_0:def 4;
      then
A2:   ex p st p = a & p`1 <= 1 & p`1 >= 0 & p`2 = 1;
      a in LSeg(|[1,0]|,|[1,1]|) by A1,XBOOLE_0:def 4;
      then ex p2 st p2 = a & p2`1 = 1 & p2`2 <= 1 & p2`2 >= 0 by Th13;
      hence thesis by A2,EUCLID:53;
    end;
    assume
A3: a = |[1,1]|;
    then
A4: a in LSeg(|[1,0]|,|[1,1]|) by RLTOPSP1:68;
    a in LSeg(|[0,1]|,|[1,1]|) by A3,RLTOPSP1:68;
    hence thesis by A4,XBOOLE_0:def 4;
  end;
  hence thesis by TARSKI:def 1;
end;
