Let E -> M a fiber bundle.  Then ProjectionTransformation(n, m) defines the canonical projection map from J^n(E) to J^m(E).

The command ProjectionTransformation is part of the DifferentialGeometry:-JetCalculus package.  It can be used in the form ProjectionTransformation(...) only after executing the commands with(DifferentialGeometry) and with(JetCalculus), but can always be used by executing DifferentialGeometry:-JetCalculus:-ProjectionTransformation(...).