If you have 3 apples, you take away 2, how many apples do you have? 1 of course! But then again, you took away 2, so therefore you should have 2. The question is ambiguous depends on how you interpret the words ‘have’ and ‘take-away’. Compare that to something like this: def apples_you_have (total_apples, apples_you_took_away): return total_apples - apples_you_took_away...
Just a collection of stuff (mostly from my old blog)