21. Mostow rigidity was also used by Thurston to prove the uniqueness of triangulated planar graphs . 22. Consequently, only planar graphs have duals. 23. However, there are infinitely many 3-connected well-covered maximal planar graphs . 24. An alternating knot diagram is in one-to-one correspondence with a planar graph . 25. The problem admits a PTAS for special cases such as unit disk graphs and planar graphs . 26. That is, these two graphs are the only minor-minimal non-planar graphs . 27. The planar separator theorem states that a similar partition can be constructed in any planar graph . 28. Such graphs are called planar graphs . 29. Among planar graphs , the truncated cuboctahedral and truncated icosidodecahedral graphs are also zero-symmetric. 30. Similarly, an embedding of a rooted planar graph can be encoded as a blossom tree.
