A generalisation of tt-designs

This paper defines a class of designs which generalise tt-designs, resolvable designs, and orthogonal arrays. For the parameters t=2,k=3t=2,k=3 and λ=1λ=1, the designs in the class consist of Steiner triple systems, Latin squares, and 1-factorisations of complete graphs. For other values of tt and kk, we obtain tt-designs, Kirkman systems, large sets of Steiner triple systems, sets of mutually orthogonal Latin squares, and (with a further generalisation) resolvable 2-designs and indeed much more general partitions of designs, as well as orthogonal arrays over variable-length alphabets.The Markov chain method of Jacobson and Matthews for choosing a random Latin square extends naturally to Steiner triple systems and 1-factorisations of complete graphs, and indeed to all designs in our class with t=2,k=3t=2,k=3, and arbitrary λλ, although little is known about its convergence or even its connectedness.