Forward arbitrage means that the price ratio between futures and spot is higher than the upper limit of no-arbitrage range, and arbitrageurs can sell futures and buy spot with the same value at the same time. After the current spot price ratio falls back to the no-arbitrage range, they will close their positions at the same time to obtain arbitrage income.

Reverse arbitrage means that when the price ratio between futures and spot is lower than the lower limit of the no-arbitrage interval, the arbitrageur can buy futures with the same value and sell spot with the same value at the same time. When the price ratio between futures and spot rises to the no-arbitrage interval, the futures and spot are closed at the same time to obtain arbitrage income.

5- 1 and 9- 1 refer to contracts, for example, 5 refers to May contracts.