  To study orthogonal arrays and signed orthogonal arrays, Ray-Chaudhuri and
Singhi (1988 and 1994) considered some module spaces. Here, using a linear
algebraic approach we define an inclusion matrix and find its rank. In the
special case of Latin squares we show that there is a straightforward algorithm
for generating a basis for this matrix using the so-called intercalates. We
also extend this last idea.
