A Simple Proof of the Bichteler-Dellacherie Theorem

We give a simple and rather elementary proof of the celebrated Bichteler-Dellacherie-Mokobodzki Theorem, which states that a process S is a good integrator if and only if it is a semimartingale. As a corollary, we obtain a characterization of semimartingales along the lines of classical Riemann integrability.