  Motivated by the considerable success of alternative theories of gravity, we
consider the toy model of a higher derivative Lagrangian theory, namely the
Pais-Uhlenbeck oscillator studied in a recent paper by Hawking-Hertog. Its
Euclidean Path Integral is studied with a certain detail and a pedagogical
derivation of the propagator, which makes use of a Theorem due to Forman, is
consequently proposed
