  Let $M$ be an uniformizable Anderson $t$-motive. We can describe its lattice
as an element of the maximal Schubert cycle of its flag variety. This element
(called a Siegel element) is a set of matrices parametrized by integer points
of a tetrahedron. We give explicit formulas for a Siegel element for $M'$ --
the dual of $M$. As a by-product, we get another proof of the theorem that the
lattice of $M'$ is the dual of the lattice of $M$, independent of the proof
obtained by U. Hartl and A.-K. Juschka. Generalizations of this result to
non-maximal Schubert cycles, other tensor operations (tensor product and Hom)
and t-motives having non-trivial endomorphism rings, are subjects of further
research.
