On the Number of Edges in Colour-Critical Graphs and Hypergraphs.

Alexandr V. Kostochka Michael Stiebitz On the Number of Edges in Colour-Critical Graphs and Hypergraphs. 521-530 2000 20 Combinatorica 4 http://link.springer.de/link/service/journals/00493/bibs/0020004/00200521.htm db/journals/combinatorica/combinatorica20.html#KostochkaS00