convergence of a sequence with finite upcrossings
The following result characterizes convergence of a sequence in terms of finiteness of numbers of upcrossings.
Theorem.
A sequence of real numbers converges to a limit in the extended real numbers if and only if the number of upcrossings is finite for all .
Since the number of upcrossings differs from the number of downcrossings by at most one, the theorem can equivalently be stated in terms of the finiteness of .