真的吗？我觉得0是合理的。但按照wash sale的定义，day 4的sale的确是trigger wash sale了

A wash sale is a transaction in which an investor sells or trades a security at a loss and purchases "a substantially similar one" 30 days before or 30 days after the sale.

（https://www.investopedia.com/terms/w/washsale.asp#:~:text=Key%20Takeaways,to%20reduce%20their%20tax%20liability. ）

除非这个loss的能加回到day 1的cost basis里，否则这500的loss就不能claim了。 但是我不知道已经realized gain还能不能调整。