Borradaile, Le and Sherman-Bennett [ Graphs and Combinatorics , 2017] proved that every n -vertex 2-outerplane graph has a set of at least 2 n /3 vertices that induces an outerplane graph. We identify a major flaw in their proof and recover their result with a different, and unfortunately much more complex, proof.
No takes yet. Share an insight, caveat, or question.
D’Elia et al. (2026) studied this question.