Hakimi SL: On the realizability of a set of integers as degrees
of the vertices of a simple graph. *J SIAM Appl Math* 10:496-506, 1962.

PL Erdos, I Miklos and Z Toroczkai: A simple Havel-Hakimi type algorithm to
realize graphical degree sequences of directed graphs. *The Electronic
Journal of Combinatorics* 17(1):R66, 2010.