| In this paper, bounds on the cochromatic number are discussed, edge-cochromatic number of a graph is proposed, the cochromatic numbers of two kinds of line graphs and an upper bound on edge-cochromatic number of a graph which has 4l edges are obtained, properties of critically cochromatic graphs and minimally cochromatic graphs are given.The paper has five parts:1. Preliminary.2. Bounds on the cochromatic number.3. A lower bound on the cochromatic number of a kind of line graphs of triangle-free graphs and the cochromatic numbers of L(Km,n) and L(Kn).4. The criticality of cochromatic number.5. An upper bound on the edge-cochromatic number of a graph with 4l edges. |
