  A draft of a paper by Mandelbaum, "The dynamic complementarity problem", was
circulated in 1987, but has never been published. We give an exposition of two
important results from that paper which are not readily accessible in the
literature.
  The first is an example of a Skorokhod problem in two dimensions in the
quadrant for which there is not uniqueness. The second is a proof of uniqueness
for the Skorokhod problem in two dimensions in the quadrant in a critical case.
