  We consider concurrent stochastic games played on graphs with reachability
and safety objectives. These games can be solved by value iteration as well as
strategy iteration, each of them yielding a sequence of under-approximations of
the reachability value and a sequence of over-approximation of the safety
value, converging to it in the limit. For both approaches, we provide the first
(anytime) algorithms with stopping criteria. The stopping criterion for value
iteration is based on providing a convergent sequence of over-approximations,
which then allows to estimate the distance to the true value. For strategy
iteration, we bound the error by complementing the strategy iteration algorithm
for reachability by a new strategy iteration algorithm under-approximating the
safety-value.
