no. 2
A note on the zeros of exponential polynomials
Compositio Mathematica, Tome 31 (1975) no. 2, pp. 109-113. 
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     author = {Van der Poorten, A. J.},
     title = {A note on the zeros of exponential polynomials},
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     number = {2},
     year = {1975},
     mrnumber = {390188},
     zbl = {0318.30005},
     language = {en},
     url = {http://www.numdam.org/item/CM_1975__31_2_109_0/}
}
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Van der Poorten, A. J. A note on the zeros of exponential polynomials. Compositio Mathematica, Tome 31 (1975) no. 2, pp. 109-113. http://www.numdam.org/item/CM_1975__31_2_109_0/

[1] C.J. Moreno: The zeros of exponential polynomials (1). Comp. Math. vol. 26 (1973) 69-78. | Numdam | MR | Zbl

[2] R. Tijdeman: An auxiliary result in the theory of transcendental numbers. J. Number Th. 5 (1973) 80-94. | MR | Zbl