 Milliken–Taylor theorem

Fix positive integers $a_1,\dots ,a_m$. A Milliken-Taylor system generated by a sequence $x_1,x_2,\dots$ of positive integers isThe Milliken–Taylor theorem says that every finite colouring of the positive integers admits an infinite sequence $x$ for which this whole set is monochromatic. The block separation prevents the same index from contributing at two different coefficient positions. For $(a_1,a_2,a_3)=(1,2,3)$, choices $F_1=\{1,3\}$, $F_2=\{4\}$, $F_3=\{6,9\}$ give $x_1+x_3+2x_4+3x_6+3x_9$. For $m=1$, $a_1=1$, the statement is the Hindman theorem. One can also require $x$ to consist of successive disjoint block sums from any prescribed positive sequence.^[ref]

A compressed coefficient vector has no adjacent repeated entries. Two such positive coefficient vectors can be forced to produce Milliken-Taylor systems in the same colour class for every finite colouring precisely when one is a positive rational multiple of the other. Thus a finite colouring can prevent a finite-sums set and a $(1,2,3)$ Milliken-Taylor system from sharing a colour, even with different generating sequences.^[ref]

The Milliken–Taylor theorem is a result in the field of graph theory, particularly concerning the coloring of graphs. It provides a criterion for determining the chromatic number of certain types of graphs, specifically those that are constructed from the edges of a complete graph.