Non-orientable Biembeddings of Steiner Triple Systems
of Order 15
G. K. Bennett, M. J. Grannell and T. S. Griggs
Abstract.
It is shown that each possible pair of the 80
isomorphism classes of Steiner triple systems of order 15 may be
realized as the colour classes of a face 2-colourable
triangulation of the complete graph in a non-orientable surface.
This supports the conjecture that every pair of STS($n$)s, $n \ge
9$, can be biembedded in a non-orientable surface.
Compressed Postscript 
