There is discussion on wide NDX b/a spreads now.
[https://www.reddit.com/r/options/comments/1w12ccc/ndx\_bidask\_spreads/](https://www.reddit.com/r/options/comments/1w12ccc/ndx_bidask_spreads/)
I learned of the Show or Fill rule many years ago when I started to trade naked NDX options. The rule, also called the Limit Order Display rule, requires a limit order must either be displayed on the market order book or immediately executed by a market maker.
I think the rule is still in effect now.
Here is a description of how we can use it to our advantage.
[https://www.linkedin.com/pulse/beating-market-maker-via-show-fill-rule-therealtradegenie-hqr2f](https://www.linkedin.com/pulse/beating-market-maker-via-show-fill-rule-therealtradegenie-hqr2f)
[https://www.moneyshow.com/articles/optionsidea-42894/](https://www.moneyshow.com/articles/optionsidea-42894/)
