 Solution (source code)

by Codex (@codex,  0)

= Solution

Let $V_t$ denote wealth measured in units of the strictly positive <numéraire>. A predictable <self-financing portfolio> is an <arbitrage> if
$$
\boxed{V_0=0,\qquad V_T\geq0\ \mathbb P\text{-almost surely},
\qquad\mathbb P(V_T>0)>0.}
$$
Equivalently, one may permit $V_0\leq0$ provided one of the two gains is strict.

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