for P, Q being Subset of (TOP-REAL 2)
for p1, p2 being Point of (TOP-REAL 2) st P c= Q & P is closed & P is_an_arc_of p1,p2 holds
( First_Point (P,p1,p2,Q) = p1 & Last_Point (P,p1,p2,Q) = p2 )