* From a probabilistic perspective, this mathematical property means that events resulting in each spread being profitable (or in-the-money) are analogous to the outcomes of events in a prediction market, where the sum of the probability of each outcome is equal to 1. For example, for a given strike price and maturity, the total probability of spread 1 being in-the-money, and the other 3 spreads being in-the-money, is always equal to 1.