  A financial market model where agents trade using realistic combinations of
buy-and-hold strategies is considered. Minimal assumptions are made on the
discounted asset-price process - in particular, the semimartingale property is
not assumed. Via a natural market viability assumption, namely, absence of
arbitrages of the first kind, we establish that discounted asset-prices have to
be semimartingales. In a slightly more specialized case, we extend the previous
result in a weakened version of the Fundamental Theorem of Asset Pricing that
involves strictly positive supermartingale deflators rather than Equivalent
Martingale Measures.
