Let be a set of symbols, then a Howell design on symbol set is an array such that

- 1. Every cell of is either empty or contains an unordered pair of symbols from ,
- 2. Every symbol of occurs once in each row and column of , and
- 3. Every unordered pair of symbols occurs in at most one cell of .

**References**

Colbourn, C. J. and Dinitz, J. H. (Eds.) ``Howell Designs.'' Ch. 26 in
*CRC Handbook of Combinatorial Designs.*
Boca Raton, FL: CRC Press, pp. 381-385, 1996.

© 1996-9

1999-05-25