Maximal planar drawing edge lower bound
ProvedWilliamsonShmoys.maximal_planar_edge_lower_bound__p2m_1df68e30_02cf_4572_bf8a_d78917d2b48a_a1approximation-algorithmsplanar-graphstreewidth
A drawable graph on at least three vertices that has no drawable simple supergraph on the same vertex type with additional edges has at least 3n−6 edges.
Preamble
import Definitions.Def_WilliamsonShmoys_PlanarDrawingOn set_option autoImplicit false
Formal statement
theorem WilliamsonShmoys.maximal_planar_edge_lower_bound__p2m_1df68e30_02cf_4572_bf8a_d78917d2b48a_a1
{V : Type} [Fintype V] [LinearOrder V]
(L : SimpleGraph V) (hcard : 3 ≤ Fintype.card V)
(hL : WilliamsonShmoys.HasPlanarDrawingOn L)
(hmax : ∀ K : SimpleGraph V, L ≤ K →
WilliamsonShmoys.HasPlanarDrawingOn K → K = L) :
3 * Fintype.card V - 6 ≤ L.edgeSet.ncard := by sorrySource
David P. Williamson and David B. Shmoys, The Design of Approximation Algorithms, Cambridge University Press, 2011, author electronic manuscript, Section 10.2, proof of Theorem 10.11, pp. 270-272. https://doi.org/10.1017/CBO9780511921735. Bounded tree-width of the pieces: Robertson–Seymour (planar graphs of radius r have tree-width at most 3r+1) / Bodlaender (k-outerplanar graphs have tree-width at most 3k-1).