If the previous price in July was 4 130 and the price in September was 3980, then the price difference would be 150.

first

Reverse market means that under special circumstances, the spot price is higher than the futures price (or the contract price in recent months is higher than the contract price in forward months), and the basis is positive.

then

Arbitrators arbitrage by selling an advantage at a higher price and buying an advantage at a lower price. We call this arbitrage selling arbitrage.

finally

Why is it profitable to narrow the spread?

For example.

If the previous price in July is 4 130, the price difference in September is 3980, 150, the price difference in July is 4050, and the price difference in September is 4 000, then your profit is 4130-4050 = 80 4000-3980 = 20.

After thinking for a long time, I don't quite remember my major. I hope to adopt it.