theorem
  for P being Subset of TOP-REAL 2, p1,p2,q1,q2 being Point of TOP-REAL 2
  st P is_an_arc_of p1,p2 & LE q2,q1,P,p2,p1
  holds LE q1,q2,P,p1,p2 by Th18,JORDAN5B:14;
