1. Bogolyubsky, L.I., Raigorodskii, A.M.: A remark on lower bounds for the chromatic numbers of spaces of small dimension with metrics ℓ1 and ℓ2. Math Notes. 105, 180–203 (2019)
2. Croft, H.T.: Incidence incidents. Eureka (Cambridge). 30, 22–26 (1967)
3. Croft, H.T., Falconer, K.J., Guy, R.K.: Unsolved Problems in Geometry. Springer, New York (1991)
4. [De Morgan, A]: Review of the philosophy of discovery..., The Athenaeum 1694, London, pp. 501–503 (1860)
5. Erdős, P.: Some Unsolved Problems. Magyar tudomanyos akademia mathematikai kutato intezetenek közlemenyel 6 ser. A (1–2), 221–254 (1961)