T.R. Jensen and F.B. Shepherd, Note on a conjecture of Toft, Combinatorica 15, 373-377, 1995.
August 7, 1997. Tommy R. Jensen
M. Stiebitz and B. Toft, An Abstract Generalization of a Map Reduction Theorem of Birkhoff, J. Combin. Theory Ser. B 65, 165-185, 1995.
August 29, 1997. Tommy R. Jensen