let P be non empty Subset of (TOP-REAL 2); for p1, p2, q1 being Point of (TOP-REAL 2) st P is_an_arc_of p1,p2 & q1 in P & p1 <> q1 holds
Segment (P,p1,p2,p1,q1) is_an_arc_of p1,q1
let p1, p2, q1 be Point of (TOP-REAL 2); ( P is_an_arc_of p1,p2 & q1 in P & p1 <> q1 implies Segment (P,p1,p2,p1,q1) is_an_arc_of p1,q1 )
assume that
A1:
P is_an_arc_of p1,p2
and
A2:
q1 in P
and
A3:
p1 <> q1
; Segment (P,p1,p2,p1,q1) is_an_arc_of p1,q1
LE p1,q1,P,p1,p2
by A1, A2, JORDAN5C:10;
hence
Segment (P,p1,p2,p1,q1) is_an_arc_of p1,q1
by A1, A3, Th36; verum