convergent series
A series is said to be convergentif the sequence of partial sums is convergent.A series that is not convergent is said to be divergent.
A series is said to be absolutely convergentif is convergent.
When the terms of the series live in ,an equivalent condition for absolute convergence of the seriesis that all possible series obtained by rearrangementsof the terms are also convergent.(This is not true in arbitrary metric spaces.)
It can be shown that absolute convergence implies convergence.A series that converges, but is not absolutely convergent,is called conditionally convergent.
Let be an absolutely convergent series,and be a conditionally convergent series.Then any rearrangement of is convergent to the same sum.It is a result due to Riemann that can be rearranged to converge to any sum, or not converge at all.