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2. a) ZAKHAROV, V.E., SHABAT, A.B.: “Exact theory of two-dimensional self-focusing and one-dimensional self-modulation of waves in nonlinear media”. Sov. Phys. JETP 34, 62–69 (1972) [Zh.Eksp.Teor.Fiz. 161, 118(1971); b) ABLOWITZ, M.J., KAUP, D.J., NEWELL, A.C., SEGUR, H.: “The inverse scattering transform-Fourier analysis for nonlinear problems”. Studies Appl.Math. 53, 249–315(1974); c) CALOGERO, F., DEGASPERIS, A.: “Nonlinear evolution equations solvable by the inverse spectral transform, I”. Nuovo Cimento 32B, 201–242 (1976); d) CALOGERO, F., DEGASPERIS, A.: “Nonlinear evolution equations solvable by the inverse spectral transform, II”. Nuovo Cimento 39B, 1–54(1977); NEWELL; A.C.: “The general structure of integrable evolution equations”. Proc. R. Soc. Lond. A 365, 283–311(1979) CALOGERO, F., DEGASPERIS, A.: “Extension of the Spectral Transform method for solving nonlinear evolution equations, I & II”. Lett.Nuovo Cimento 22, 131–137(1978) & 22, 263–269(1978); CALOGERO, F., DEGASPERIS, A.: “Solution by the Spectral Transform method of a nonlinear evolution equation including as a special case the Cylindrical KdV Equation”. Lett. Nuovo Cimento 23, 150–154(1978).
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5. CALOGERO, F., DEGASPERIS, A.: “Reduction technique for matrix nonlinear evolution equations solvable by the Spectral Transform”. To appear in J. of Math.Phys.