XX and Ising limits in integral formulae for finite temperature   correlation functions of the XXZ chain
  We consider a multiple integral representation for a one-parameter generating function of the finite temperature $S^z$-$S^z$ correlation functions of the antiferromagnetic spin-1/2 XXZ chain in the XX limit and in the Ising limit. We show how in these limits the multiple integrals reduce to single integrals, thereby reproducing known results. 
Frank G\"ohmann and Alexander Seel