Removing matching items from a list?

[kevin4fong at gmail.com]

Thank you, Steven, for the advice. It was really helpful with the descriptions and steps.

Would you also happen to know how I could set up a list that keeps track of the removed sets?

Let's say there's 4 a's taken out. The list would show:

['a']

But if there was also 4 j's in addition to the 4 a's, it would go:

['a', 'j']

and so forth.