Optimal stopping of the maximum of an observed sequence over an order statistic of an unobserved sequence

In this paper an optimal stopping problem is considered. Only one of two sequences of random variables which are independent copies of a known continuously distributed random variable is observed. It is necessary to stop the observation at the moment in which at most k values of the unobserved sequence are greater than the observed maximum, with maximal probability. The optimal stopping rule for the finite length of the observation is obtained.