A note on the problem ¡­

A note on the problem set: s = 0 is to be interpreted that the backstop is always there, and s to infinity is to be interpreted that the backstop is never there. The text was confusing (I'm sorry) I did not intend to say that s is the time at which the existence of the backstop becomes known. It is known that at time s (which may be right now, or never) the backstop arrives.

If you are further interested in this problem, I put a paper by Michael Hoel (1978) under the additional materials (but it is not necessary to read this paper for solving the problem, it might not even be helpful as it discusses more general cases).