Arbitrage-free

In economics and finance, arbitrage (US /ˈɑːrbᵻtrɑːʒ/, UK /ˈɑːbᵻtrɪdʒ/, UK /ˌɑːbᵻtrˈɑːʒ/) is the practice of taking advantage of a price difference between two or more markets: striking a combination of matching deals that capitalize upon the imbalance, the profit being the difference between the market prices. When used by academics, an arbitrage is a (imagined, hypothetical, thought experiment) transaction that involves no negative cash flow at any probabilistic or temporal state and a positive cash flow in at least one state; in simple terms, it is the possibility of a risk-free profit after transaction costs. For instance, an arbitrage is present when there is the opportunity to instantaneously buy low and sell high.

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Wikipedia