Colouring triangle-free intersection graphs of boxes on the plane.

Alexandr V. Kostochka Irina G. Perepelitsa Colouring triangle-free intersection graphs of boxes on the plane. 243-249 2000 220 Discrete Mathematics 1-3 http://dx.doi.org/10.1016/S0012-365X(00)00027-3 db/journals/dm/dm220.html#KostochkaP00