  Working in the first order formalism of gravity, we propose an action that
combines the self and anti-self-dual parts of the curvature and comprises all
the diffeomorphism invariant Lagrangians that one can consider in this
formalism. The action that we propose is motivated by (A)dS gauge theories of
gravity. We use this action to derive the (2+1)-dimensional version of the
Immirzi parameter. Our derivation relates explicitly the Immirzi parameter to
the existence of two classically equivalent actions for the description of
gravity in (2+1) dimensions, namely the standard and exotic actions introduced
by Witten in the description of (2+1) gravity as a gauge theory. This relation
had been conjectured previously in the literature, but not derived.
