Erdős (1990). Erdős, Paul (1990), "Some of my favourite unsolved problems", in Baker, A.; Bollobás, B.; Hajnal, A. (eds.), A tribute to Paul Erdős, Cambridge University Press, pp. 467–478, ISBN0-521-38101-0, MR1117038; see in particular p. 475
Globus & Parshall (2020). Globus, Aidan; Parshall, Hans (2020), "Small unit-distance graphs in the plane", Bulletin of the Institute of Combinatorics and Its Applications, 90: 107–138, arXiv:1905.07829, MR4156400
Wormald (1979); Chilakamarri (1995); O'Donnell (1995). Wormald, Nicholas (1979), "A 4-chromatic graph with a special plane drawing", Journal of the Australian Mathematical Society, Series A, 28 (1): 1–8, doi:10.1017/S1446788700014865, MR0541161, S2CID124067465 Chilakamarri, Kiran B. (1995), "A 4-chromatic unit-distance graph with no triangles", Geombinatorics, 4 (3): 64–76, MR1313386 O'Donnell, Paul (1995), "A 40 vertex 4-chromatic triangle-free unit distance graph", Geombinatorics, 5 (1): 31–34, MR1337155
Globus & Parshall (2020). Globus, Aidan; Parshall, Hans (2020), "Small unit-distance graphs in the plane", Bulletin of the Institute of Combinatorics and Its Applications, 90: 107–138, arXiv:1905.07829, MR4156400
Erdős (1990). Erdős, Paul (1990), "Some of my favourite unsolved problems", in Baker, A.; Bollobás, B.; Hajnal, A. (eds.), A tribute to Paul Erdős, Cambridge University Press, pp. 467–478, ISBN0-521-38101-0, MR1117038; see in particular p. 475
Wormald (1979); Chilakamarri (1995); O'Donnell (1995). Wormald, Nicholas (1979), "A 4-chromatic graph with a special plane drawing", Journal of the Australian Mathematical Society, Series A, 28 (1): 1–8, doi:10.1017/S1446788700014865, MR0541161, S2CID124067465 Chilakamarri, Kiran B. (1995), "A 4-chromatic unit-distance graph with no triangles", Geombinatorics, 4 (3): 64–76, MR1313386 O'Donnell, Paul (1995), "A 40 vertex 4-chromatic triangle-free unit distance graph", Geombinatorics, 5 (1): 31–34, MR1337155
Wormald (1979); Chilakamarri (1995); O'Donnell (1995). Wormald, Nicholas (1979), "A 4-chromatic graph with a special plane drawing", Journal of the Australian Mathematical Society, Series A, 28 (1): 1–8, doi:10.1017/S1446788700014865, MR0541161, S2CID124067465 Chilakamarri, Kiran B. (1995), "A 4-chromatic unit-distance graph with no triangles", Geombinatorics, 4 (3): 64–76, MR1313386 O'Donnell, Paul (1995), "A 40 vertex 4-chromatic triangle-free unit distance graph", Geombinatorics, 5 (1): 31–34, MR1337155