no. 2
A directional compactification of the complex Fermi surface
Compositio Mathematica, Tome 79 (1991) no. 2, pp. 205-229. 
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     author = {B\"attig, Daniel and Kn\"orrer, Horst and Trubowitz, Eugene},
     title = {A directional compactification of the complex {Fermi} surface},
     journal = {Compositio Mathematica},
     pages = {205--229},
     publisher = {Kluwer Academic Publishers},
     volume = {79},
     number = {2},
     year = {1991},
     mrnumber = {1117340},
     zbl = {0754.58038},
     language = {en},
     url = {http://www.numdam.org/item/CM_1991__79_2_205_0/}
}
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Bättig, Daniel; Knörrer, Horst; Trubowitz, Eugene. A directional compactification of the complex Fermi surface. Compositio Mathematica, Tome 79 (1991) no. 2, pp. 205-229. http://www.numdam.org/item/CM_1991__79_2_205_0/

[Bä] D. Bättig, A toroidal compactification of the Fermi surface for the discrete Laplace operator. Preprint, ETH Zürich 1989.

[Bo] G. Borg, Eine Umkehrung der Sturm-Liouvilleschen Eigenwertaufgabe, Acta Math. 78, 1-96 (1946). | MR | Zbl

[KT] H. Knörrer, E. Trubowitz, A directional compactification of the complex Bloch variety. Comm. Math. Helvetici 65, 114-149 (1990). | MR | Zbl

[SM] C. Siegel, J. Moser, Lectures on Celestial Mechanics, Springer-Verlag 1979. | MR