By the Grunbaum-Aksenov Theorem (extending Grotzsch's Theorem) every planar graph with at most three triangles is 3-colorable. However, there are infinitely many planar 4-critical graphs with exactly four triangles. We describe all such graphs. This answers a question of Erdos from 1990. (C) 2014 Elsevier Ltd. All rights reserved.
机构:
Ayya Nadar Janaki Ammal Coll, Ctr Res & Post Grad Studies Math, Sivakasi 626124, Tamil Nadu, IndiaAyya Nadar Janaki Ammal Coll, Ctr Res & Post Grad Studies Math, Sivakasi 626124, Tamil Nadu, India
Kathiresan, K. M.
Muthukamatchi, R.
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机构:
Ayya Nadar Janaki Ammal Coll, Ctr Res & Post Grad Studies Math, Sivakasi 626124, Tamil Nadu, IndiaAyya Nadar Janaki Ammal Coll, Ctr Res & Post Grad Studies Math, Sivakasi 626124, Tamil Nadu, India
Muthukamatchi, R.
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