We study the particle content of higher derivative theories of gravity built
    with contractions of the Riemann tensor and its covariant derivatives. In the
    absence of the latter, there is a family of theories exhibiting an Einsteinian
    spectrum known as generalized quasi-topological gravities. In turn, we present
    a no-go result for the construction of Einsteinian gravities involving
    covariant derivatives of the Riemann tensor. We find evidences suggesting that
    (truncated series) finite order Lagrangians with covariant derivatives of the
    Riemann tensor generically present ghosts in their spectrum. This might be
    interpreted as a hint of non-locality in any healthy UV completion of General

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