A tetrahedral curve is a (usually nonreduced) curve in P^3 defined by an
unmixed, height two ideal generated by monomials. We characterize when these
curves are arithmetically Cohen-Macaulay by associating a graph to each curve
and, using results from combinatorial commutative algebra and Alexander
duality, relating the structure of the complementary graph to the
Cohen-Macaulay property.Comment: 15 pages; minor revisions to v. 1 to improve clarity; to appear in
  JPA