Forward market means that the futures price is higher than the spot price at that time or the forward contract price is higher than the recent contract price.

Niusan actually buys recent contracts and sells forward futures contracts at the same time, relying on the narrowing of the basis to make profits;

Bear market arbitrage is to sell recent futures contracts and buy forward contracts at the same time, relying on the expansion of basis to make profits.

The bull spread in the positive market actually belongs to selling arbitrage, while the bear market arbitrage in the positive market belongs to buying arbitrage.

That's it.