Book

Bryant, Victor (1993) Aspects of combinatorics: a wide-ranging introduction. Cambridge University Press, Cambridge England; New York, NY, USA. ISBN 978-0521429979

Spencer, Lyle M. and Spencer, Signe M. (1993) Competence at Work: models for superior performance 1st Edition. John Wiley & Sons, Toronto, Canada. ISBN 978-0471548096

Victor, Bryant (1993) Aspects of Combinatorics : a wide-ranging introduction. Cambridge University Press, Cambridge, pp. 1-14. ISBN 0-521-42997-8