Degeneracy of the ground-state of antiferromagnetic spin-1/2 HamiltoniansG. Misguich, C. Lhuillier, M. Mambrini and P. SindzingreEur. Phys. J. B, 26 2 (2002) 167-183DOI: https://doi.org/10.1140/epjb/e20020078