[1] Fokas A S, Santini P M. The recursion operator of the Kadomtsev-Petviashvili equation and the squared eigenfunctions of the Schr¨odinger operator. Stud Appl Math, 1986, 75: 179–185

[2] Fokas A S, Santini PM. Recursion operators and bi-Hamiltonian structures in multidimensions II. Commun Math Phys, 1988, 116: 449–474

[3] Matsukidaira J, Satsuma J, Strampp W. Conserved quantities and symmetries of KP hierarchy. J Math Phys, 1990, 31: 1426–1434

[4] Fuchssteiner B, Fokas A S. Symplectic structures, their B¨acklund transformation and hereditary symmetries. Phys D, 1981, 4: 47–66

[5] Olver P J. Applications of Lie Groups to Differential Equations. New York: Springer-Verlag, 1986

[6] Santini P M, Fokas A S. Recursion operators and bi-Hamiltonian structures in multidimensions I. Commun Math Phys, 1988, 115: 375–419

[7] Strampp W, Oevel W. Recursion operators and Hamitonian structures in Sato theory. Lett Math Phys, 1990, 20: 195–210

[8] Stephen C A. Bi-Hamiltonian operators, integrable flows of curves using moving frames and geometric map equations. J Phys A: Math Gen, 2006, 39: 2043–2072

[9] Cheng Y. Constraints of the Kadomtsev-Petviashvili hierarchy. J Math Phys, 1992, 33: 3774–3782

[10] Loris I. Recursion operator for a constraint BKP system//Boiti M, Martina L, et al, eds. Proceedings of the Workshop on Nonlinearity, Integrability and All That Twenty years After NEEDS’79. Singapore: World Scientific, 1999: 325–330

[11] Gurses M, Karasu A, Sokolov V V. On construction of recursion operators from Lax representation. J Math Phys, 1999, 40: 6473–6490

[12] Loris I, Willox R. Bilinear form and solutions of the k-constrained Kadomtsev-Petviashvili hierarchy. Inverse Problems, 1997, 13: 411–420

[13] Loris I. Symmetry reductions of the BKP hierarchy. J Math Phys, 1999, 40: 1420–1431

[14] Loris I. Bilinear representation of integrable equation. Theor Math Phys, 2002, 133: 1549–1556

[15] He J S, Wu Z W, Cheng Y. Gauge transformations for the constrained CKP and BKP hierarchies. J Math Phys, 2007, 48: 113–519

[16] Date E, Kashiwara M, Jimbo M, Miwa T. Transformation groups for soliton equations//Jimbo M, Miwa T, ed. Nonlinear Integrable Systems-Classical and Quantum Theory. Singapore: World Scientific, 1983: 39–119

[17] Dickey L A. Soliton equations and Hamiltonian Systems. 2nd ed. Singapore: World Scintific, 2003

[18] Date E, Kashiwara M, Jimbo M, Miwa T. KP hierarchy of orthogonal symplectic type transformation groups for soliton equations VI. J Phys Soc Japan, 1981, 50: 3813–3818

[19] Kaup D J. On the inverse scattering problem for cubic eigenvalue problems of the class 3x+6Qx+6R =. Stud Appl Math, 1980, 62: 189–216

[20] Kupershmidt B A. A super Korteweg-de Vires equation: an integrble system. Phys Lett A, 1984, 102: 213–215

[21] Konopelchenko B G, Sidorenko J, Strampp W. (1 + 1)-dimensional integrable systems as symmetry constraints of (2 + 1)-dimensional systems. Phys Lett A, 1991, 157: 17–21

[22] Cheng Y, Li Y S. The constraint of the Kadomtsev-Petviashvili equation and its special solutions. Phys Lett A, 1991, 157: 22–26

[23] Loris I. On reduced CKP equations. Inverse Problems, 1999, 15: 1099–1109

[24] Olver P J. Evolution equations possessing infinitely many symmetries. J Math Phys, 1977, 18: 1212–1215

[25] Ito M. An extension of nonlinear evolution equations of the KdV(mKdV) type to higher orders. J Phys Soc Japan, 1980, 49: 771–778

[26] Aratyn H, Nissimov E, Pacheva S. Constrained KP hierarchies: additional symmetries, Darboux-B¨acklund solutions and relations to multi-matrix models. Int J Mod Phys A, 1997, 12: 1265–1340

[27] Adler M. On the B¨acklund transformation for the Gel’fand-Dickey equations. Commun Math Phys, 1981, 80: 517–527