Kogan, I. A. and Moreno Maza, M.
Computation of canonical forms for ternary cubics.
Proceedings of International Symposium on Symbolic and Algebraic Computation (ISSAC), ACM, (2002), 151 - 160.
Corrected version
Corrections to published version Maple worksheet
Invariant Euler-Lagrange equations and the invariant variational
bicomplex.
Acta Applicandae Mathematicae, Vol. 76, No. 2,
(2003), 137 - 193.
Corrected version Corrections to published version.   Maple worksheet: iVB