Let G be a Sylow p-subgroup of the unitary groups GU(3, q2),
GU(4, q2), the symplectic group Sp(4, q) and, for q odd, the
orthogonal group O +(4, q). In this paper we construct a presenta tion for the invariant ring of G acting on the natural module.
In particular we prove that these rings are generated by orbit
products of variables and certain invariant polynomials which
are images under Steenrod operations, applied to the respective
invariant form defining the corresponding classical group. We also
show that these generators form a SAGBI basis and the invariant
ring for G is a complete intersection.info:eu-repo/semantics/publishedVersio
