  Expanding General Relativity in the inverse speed of light, 1/c, leads to a
nonrelativistic gravitational theory that extends the Post-Newtonian expansion
by the inclusion of additional strong gravitational potentials. This theory has
a fully covariant formulation in the language of Newton-Cartan geometry but we
revisit it here in a 3+1 formulation. The appropriate 3+1 formulation of
General Relativity is one first described by Kol and Smolkin (KS), rather than
the better known Arnowitt-Deser-Misner (ADM) formalism. As we review, the KS
formulation is dual to the ADM formulation in that the role of tangent and
co-tangent spaces get interchanged. In this 3+1 formulation the 1/c expansion
can be performed in a more systematic and efficient fashion, something we use
to extend the computation of the effective Lagrangian beyond what was
previously achieved and to make a number of new all order observations.
