theorem Th21: :: JORDAN16:21

for A being Subset of (TOP-REAL 2)
for p1, p2, q1, q2 being Point of (TOP-REAL 2) st A is_an_arc_of p1,p2 & LE q1,q2,A,p1,p2 & q1 <> q2 holds
Segment (A,p1,p2,q1,q2) is_an_arc_of q1,q2