Item from Mathematical Reviews (American Mathematical Society)--access their stable url through the AMS database via an institutional library:

MR1835275 (2002b:90025) Alpern, Steve; Howard, J. V. Alternating search at two locations. Dynam. Control 10 (2000), no. 4, 319--339 (2001). (Reviewer: Sandra L. Arlinghaus) 90B40 (90C35 93C15)