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3. A. P. Veselov and S. P. Novikov, "Finite-zone two-dimensional Schr�dinger operators. Distinguishing potential operators. Real theory," Dokl. Akad. Nauk SSSR,279, No. 1, 20?24 (1984).
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5. S. P. Novikov and A. P. Veselov, "Two-dimensional Schr�dinger operator: Inverse scattering transform and nonlinear equations," in: Solitons and Coherent Structures, North-Holland, Amsterdam (1986), pp. 267?273 (for the 60th birthday of Martin Kruskal).