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10 votes
2 answers
782 views

Graphs with many edges avoided by Hamiltonian cycles

Let $G$ be a $3$-connected Hamiltonian graph with at least one edge that belongs to each H-cycle of $G$. Some authors (e.g. in the link given here) call such an edge an a-edge and an edge that belongs ...
Wolfgang's user avatar
  • 13.4k
15 votes
2 answers
2k views

What is the smallest uniquely hamiltonian graph with minimum degree at least 3?

I would like to know more about uniquely hamiltonian graphs with minimum vertex degree at least 3, and in particular what is the smallest one. (Recall that a graph is hamiltonian if it has a cycle ...
Gordon Royle's user avatar
  • 12.7k
5 votes
1 answer
279 views

Infinitely many counterexamples to Nash-Williams's conjecture about hamiltonicity?

Question from 2013 gives one counterexample to Nash-Williams's conjecture about hamiltonicity of dense digraphs. Later, we found tens of counterexamples on more than 30 vertices and believe there are ...
joro's user avatar
  • 25.4k
5 votes
0 answers
99 views

Graph gadget related to uniquely hamiltionian regular graphs

A graph is uniquely hamiltonian if it has exactly one hamiltonian cycle. According to a conjecture there are no $r$-regular uniquely hamiltonian graphs for $r > 2$ and of special interest is the ...
joro's user avatar
  • 25.4k
2 votes
0 answers
116 views

Two more counterexamples to a conjecture from 1975 about hamiltonicity of digraphs

Question from 2013 gives one counterexample to Nash-Williams's conjecture 1975 about hamiltonicity of dense digraphs. In the linked answer, @LouisD "reverse engineered" the counterexample ...
joro's user avatar
  • 25.4k