On-Line Selection of Alternating Subsequences from a Random Sample
  We consider sequential selection of an alternating subsequence from a sequence of independent, identically distributed, continuous random variables, and we determine the exact asymptotic behavior of an optimal sequentially selected subsequence. Moreover, we find (in a sense we make precise) that a person who is constrained to make sequential selections does only about 12% worse than a person who can make selections with full knowledge of the random sequence. 
Alessandro Arlotto, Robert W. Chen, Lawrence A. Shepp, J. Michael   Steele
math.PR math.OC