Edge partitions of the Rado graph

We will prove that for every colouring of the edges of the Rado graph, (that is the countable homogeneous graph), with finitely many coulours, it contains an isomorphic copy whose edges are coloured with at most two of the colours. It was known 4] that there need not be a copy whose edges are coloured with only one of the colours. For the proof we use the lexicographical order on the vertices of the Rado graph, defined by Erdös, Hajnal and Pósa.Using the result we are able to describe a Ramsey basis for the class of Rado graphs whose edges are coloured with at most a finite number,r, of colours. This answers an old question of M. Pouzet.Supported by the French PRC Math-Info.Supported by NSERC of Canada Grant # 691325.