User Input Set Difference w/ Characters

I'm looking to create a program that takes a set of 10 user input characters(could be numbers, letters, symbols) in two sets and gives me the difference.

A = {a, b, c, d}
B = {b, c}

A - B would return {a, d}

I've looked into set difference but do not understand it all that well. All examples I could find used only numbers and were given(not user input).

Is it possible to do with with my needs?
Is there a simpler way to do it?
If someone could provide me with a example of set difference using user input, I'd appreciate it.

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