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I. M. VITEBSKII, O. D. KOLOTII, N. M. LAVRINENKO, V. P. SEMINOZHENKO, and V. L. SOBOLEV, Magnetic symmetry and phase transitions in the tetragonal YBa2Cu3O6+x, Low Temp. Phys. 16, (1990) [Fiz. Nizk. Temp. 16, 667-672, (1990)].