Solution:
Let A1A2…An be a convex n-gon. Denote by B the set of the connected vertices and let B1B2…Bk be its convex hull. We shall prove by induction on n that there is a map with the desired properties that in addition sends two given adjacent vertices of the n-gon to two given adjacent vertexes of B1B2…Bk.
The base of the induction n=3 is obvious. Suppose that our statement is true for any k<n. To prove it for n, it is enough to find a map for n that sends A1 and A2 to B1 and B2, respectively. Note that there is a unique point Ai that is connected with A1 and A2 (otherwise, some segments will have a common interior point). Consider the points X1,X2,…,Xs from B such that any of the triangles B1XiB2 contains no points of B. It is easy to find a point among them, say Xl, such that the interiors of B 1 B 2 X l and B 2 B 1 X l contain at most n−i and i−3 points of B, respectively. It is clear now that there are a line through Xl and an interior point of the segment B1B2 that divides the set B into two subsets B1 and B2, containing n−i+1 and i−2 points, respectively. Let B1Xl and B2Xl be sides of the convex hulls of these two sets. If Ai is the corresponding point to Xl, then applying the induction assumption to the sets A2A3…Ai and B2∪{Xl}, and to AiAi+1…AnA1 and B1∪{Xl}, we see that the statement is true for n points. This completes the solution of the problem.