O. Aichholzer, T. Hackl, D. Orden, A. Pilz, M. Saumell, and
B. Vogtenhuber
In this paper we consider the flip operation for combinatorial pointed
pseudo-triangulations where faces have size 3 or 4, so-called
combinatorial 4-PPTs. We show that every combinatorial 4-PPT is
stretchable to a geometric pseudo-triangulation, which in general is not the
case if faces may have size larger than 4. Moreover, we prove that the flip
graph of combinatorial 4-PPTs with triangular outer face is connected and has
diameter

.