  We prove the main conjecture of the paper ``On the expected value of the
minimum assignment'' by Marshall W. Buck, Clara S. Chan, and David P. Robbins
(Random Structures & Algorithms 21 (2002), no. 1, 33--58). This is a vast
generalization of a formula conjectured by Giorgio Parisi for the $n$ by $n$
random assignment problem.
  We combine the urn model from the article by Buck, Chan and Robbins, with our
proof of Parisi's conjecture in our article posted on the Arxiv in March this
year. Our new theorem generalize simultaneously our main theorem from that
article and the conjecture by Buck, Chan and Robbins. Using the urn model we
avoid several technical difficulties from our previous proof of Parisi's
conjecture and get a shorter proof in a conceptually more appealling setting.
