Peter J. Olver is a mathematician at the University of Minnesota in Minneapolis. His interests include the application of the Lie theory to dynamical systems, Hamiltonian systems, variational calculus, invariant theory
books by Peter Olver: complete list
The following two books have much overlap with some topics in $n$lab:
Applications of Lie groups to differential equations, Springer (few editions);
Equivalence, invariants, and symmetry, Cambridge Univ. Press 1995.