Invariant Variational Calculus:
Kogan, I. A. and Olver, P.
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
Kogan, I. A. and Olver, P.
The invariant variational bicomplex.
Contemporary Mathematics, AMS, Vol. 285, (2001), 131 - 144.
Corrected version Corrections to published version