The problem is:
Give an example of a convergent series such that, when the terms are rearranged, the series sums to a different value.
A solution is:
Although everything makes sense in this solution, I don't get how what it claims is possible. How can a series have two different sums?
Is this caused by the fact that subtraction is not commutative or associative? Hence, in fact, we really have two different series here?