##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
summary
Three lessons:
Set difference is not symmetric: $A \setminus B \neq B \setminus A$.
You can compute both differences independently.
Always convert to sets when the problem asks for unique elements.
If you see "elements in one but not the other," you need set difference.
