An arbitrage is a portfolio that costs nothing or less, never pays a negative amount, and is not identically worthless: , , and at least one of the inequalities strict (, or ). The market has no arbitrage when no such portfolio exists.
Ejemplos
Example 1.9 (A binomial market)
A bond costs 0.98 and pays 1; a share costs 100 and pays 120 or 90. The equations and give , , both positive: no arbitrage. The risk-neutral probability of the up state is , whatever its real-world probability. A call struck at 100 pays and is worth .