2. The principle is different: when the bull spread is carried out, the spread between contracts is narrowed, and the bear market arbitrage needs to expand profits through the spread.
3. Different returns: the return of bull market spread = opening spread-closing spread, and the arbitrage return of bear market = closing spread-opening spread.
In fact, the profit of arbitrage is based on the change of price difference, so where does the opportunity of arbitrage come from? The price difference is generally determined by the holding cost between two different delivery months, and the holding cost is determined by storage space, interest and insurance premium. If the price difference between the near-month contract and the far-month contract deviates from the normal period, and the holding cost has not changed significantly, then there will be room for arbitrage.