An extremality of the translation-invariant Gibbs measure for the   HC-model on a Cayley tree
  In this paper we study the extremality of translation-invariant Gibbs measure for the HC-model on a Cayley tree. It is known that for this model the translation-invariant measure is unique. We give a new proof of this statement and found regions of the extremality of this measure on the Cayley tree of order k. 
U.A. Rozikov, R.M. Khakimov
math-ph math.MP