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 process, we s…
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4 results for “2-apex”
New proof for graphs with 21 edges not 2-apex.
problem Identifying graphs with 21 edges that are not 2-apex.
method Combination of triangle-Y and Y-triangle moves on K7, proving minor minimal properties.
result The 20 Heawood family and 7 Petersen family are minor minimal for not 2-apex and not apex properties.
We show that the 14 graphs obtained by moves on K_7 constitute a complete list of the minor minimal intrinsically knotted graphs on 21 edges. We also present evidence in support of a conjecture that the 20 graph Heawood family, obtained by a combination of and mo…
Constructions stemming from non-separating planar graphs and their Colin de Verdière invariantmath.CO
New constructions from non-separating planar graphs improve understanding of graph linkability and knotability.
problem Understanding linkability and knotability of graph complements.
method Using maximal non-separating planar graphs to construct examples of maximal linkless and knotless graphs, and analyzing their Colin de Verdière invariant.
result The Colin de Verdière invariant of the complement of a maximal non-separating planar graph satisfies μ(cG) ≤ n-4, and equality holds.