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Alavi, Y.; Lick, D. R.; White, A. T. . (1972). [Lecture Notes in Mathematics] Graph Theory and Applications Volume 303 || On limit points of spectral radii of non-negative symmetric integral matrices. , 10.1007/BFb0067350(Chapter 17), 165–172. doi:10.1007/BFb0067367 
An interview with Sci-Hub Founder Alexandra Elbakyan,Who exactly should pay for academic research