Umbral interpolation and the addition/contraction tree for graphs. - Nigel Ray; Colin Wright (Discret. Math., 1992)

Ultimate chromatic polynomials. - Nigel Ray; William Schmitt (Discret. Math., 1994)

Chromatic polynomials of partition systems. - Cristian Lenart; Nigel Ray (Discret. Math., 1997)

Hopf algebras of set systems. - Cristian Lenart; Nigel Ray (Discret. Math., 1998)