Graphs of 20 edges are 2–apex, hence unknotted
Graphs of 20 edges are 2–apex, hence unknotted
A graph is 2-apex if it is planar after the deletion of at most two vertices.Such graphs are not intrinsically knotted, IK.We investigate the converse, does not IK imply 2-apex?We determine the simplest possible counterexample, a graph on nine vertices and 21 edges that is neither IK nor 2-apex.In the …