  In his pioneering work on singular shells in general relativity, Lanczos had
derived jump conditions across energy-momentum carrying hypersurfaces from the
Einstein equation with codimension 1 sources. However, on the level of the
action, the discontinuity of the connection arising from a codimension 1
energy-momentum source requires to take into account two adjacent space-time
regions separated by the hypersurface.
  The purpose of the present note is to draw attention to the fact that
Lanczos' jump conditions can be derived from an Einstein action but not from an
Einstein-Hilbert action.
