J. Richter et al., GROUND-STATE PHASE-RELATIONSHIPS AND LEVEL ORDERING FOR FRUSTRATED QUANTUM ANTIFERROMAGNETS, Journal of low temperature physics, 99(3-4), 1995, pp. 363-365
We present arguments in favor of the suggestion that the Marshall-Peie
rls phase relationships and the Lieb-Mattis level ordering survive the
frustration in the square-lattice Heisenberg antiferromagnet for rela
tively strong frustration parameters.