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Demaine & Hajiaghayi (2004b). Demaine, Erik D.; Hajiaghayi, MohammadTaghi (2004b), "Equivalence of local treewidth and linear local treewidth and its algorithmic applications", Proceedings of the Fifteenth Annual ACM-SIAM Symposium on Discrete Algorithms, New York: ACM, pp. 840–849, MR2290974.
Kao (2008). Kao, Ming-Yang, ed. (2008), "Treewidth of graphs", Encyclopedia of Algorithms, Springer, p. 969, ISBN9780387307701, Another long-standing open problem is whether there is a polynomial-time algorithm to compute the treewidth of planar graphs.
Lagergren (1993). Lagergren, Jens (1993), "An upper bound on the size of an obstruction", Graph structure theory (Seattle, WA, 1991), Contemporary Mathematics, vol. 147, Providence, RI: American Mathematical Society, pp. 601–621, doi:10.1090/conm/147/01202, ISBN9780821851609, MR1224734.