Could we define a map from vector<int>::iterator to int? What about from list<int>::iterator to int? In each case, if not, why not

We can define `map<vector<int>::iterator, int>` because the iterator of vector supports iterator arithmetic which includes `<` operator.

But we cannot define `map<list<int>::iterator, int>` because the iterator of list does not support iterator arithmetic and does not support `<` operator.