Physics in (canonical) quantum gravity needs to be manifestly
    diffeomorphism-invariant. Consequently, physical observables need to be
    formulated in terms of manifestly diffeomorphism-invariant operators, which are
    necessarily composite. This makes an evaluation in general involved, even if
    the concrete implementation of quantum gravity should be treatable
    (semi-)perturbatively in general. A mechanism developed by Fr\”ohlich, Morchio
    and Strocchi for flat-space-time quantum field theory may also be applicable in
    this case. It may be possible to test this mechanism with methods like
    dynamical triangulation.

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