Simplify level-cycle search table
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@@ -1345,6 +1345,35 @@ $S \subseteq V(G)$ such that $G$ admits a proper $4$-vertex-colouring
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with the level-cycle three-colour restriction with respect to $S$.
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with the level-cycle three-colour restriction with respect to $S$.
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\end{conjecture}
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\end{conjecture}
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\subsection*{Enumeration for small $n$}
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We exhaustively enumerated all plane triangulation isomorphism classes with
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$4 \leq n \leq 12$ vertices and, for each graph, searched the vertex sources
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in order until a witness colouring was found or every source had been tested.
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No counterexample to Conjecture~\ref{conj:level-cycle-three-colour} appeared
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in this range. Table~\ref{tab:level-cycle-three-colour-counts} records the
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size of the search space and the amount of source-search work required.
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\begin{table}[ht]
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\centering
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\small
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\setlength{\tabcolsep}{4pt}
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\begin{tabular}{cccc}
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$n$ & triangulations & with witness & source checks \\\hline
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$4$ & $1$ & $1$ & $1$ \\
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$5$ & $1$ & $1$ & $1$ \\
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$6$ & $2$ & $2$ & $2$ \\
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$7$ & $5$ & $5$ & $5$ \\
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$8$ & $14$ & $14$ & $14$ \\
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$9$ & $50$ & $50$ & $50$ \\
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$10$ & $233$ & $233$ & $237$ \\
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$11$ & $1249$ & $1249$ & $1296$ \\
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$12$ & $7595$ & $7595$ & $8069$ \\
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\end{tabular}
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\caption{Exhaustive vertex-source search for the level-cycle three-colour conjecture on all triangulation isomorphism classes with $4 \leq n \leq 12$. Every triangulation in this range admits at least one vertex source witnessing the conjecture.}
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\label{tab:level-cycle-three-colour-counts}
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\end{table}
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\begin{definition}[Seam]
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\begin{definition}[Seam]
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\label{def:seam}
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\label{def:seam}
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A \emph{seam} of a maximal planar graph $G$ is a simple cycle
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A \emph{seam} of a maximal planar graph $G$ is a simple cycle
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