## Howell Design

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.