theorem Th3:
  q in A implies q in L_Segment(A,p1,p2,q)
proof
  assume q in A;
  then
A1: LE q,q,A,p1,p2 by JORDAN5C:9;
  L_Segment(A,p1,p2,q) = {q1 : LE q1,q,A,p1,p2} by JORDAN6:def 3;
  hence thesis by A1;
end;
