Added a brief indication.

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- Noam Zeilberger,
*Linear lambda terms as invariants of rooted trivalent maps*(arXiv:1512.06751).

added this pointer (hat tip to David C. here):

On the logical equivalence between the four-colour theorem and a statement about transition from the small N limit to the large N limit for Lie algebra weight systems on Jacobi diagrams via the ’t Hooft double line construction:

- Dror Bar-Natan,
*Lie Algebras and the Four Color Theorem*, Combinatorica 17-1(1997) 43–52 (arXiv:q-alg/9606016, doi:10.1007/BF01196130)