  We clarify the relationship between works of Lee-Szczarba and Ash-Rudolph on
the homology of the Steinberg module of a linear Tits building. This yields a
simple proof of the Solomon-Tits theorem in this special case. We also give a
(weak) relationship between this combinatorics and the one studied by van der
Kallen, Suslin and Nesterenko to compute the homology of the general linear
group with constant coefficients.
