Duque, F., H. González-Aguilar, C. Hernández-Vélez, J. Leaños, and C. Medina. “The Complexity of Computing the Cylindrical and the $t$-Circle Crossing Number of a Graph”. The Electronic Journal of Combinatorics, Vol. 25, no. 2, June 2018, p. P2.43, doi:10.37236/7193.