  For a manifold $M$ endowed with a Legendrean (or Lagrangean) contact
structure $E\oplus F \subset TM$, we give an elementary construction of an
invariant partial connection on the quotient bundle $TM/F$. This permits us to
develop a na\"{i}ve version of relative tractor calculus and to construct a
second order invariant differential operator, which turns out to be the first
relative BGG operator induced by the partial connection.
