The projective plane crossing number of C3 × Cn

In this paper, we show that the projective plane crossing number of the graphs C₃ × C_n is n - 1 for n ≤ 5 and 2 for n = 4. As far as we can tell from the literature, this is the first infinite family of graphs whose crossing number is known on a single surface other than the plane. © 1993 John Wiley & Sons, Inc.