Laurinčikas, Antanas, and Kohji Matsumoto. “On Estimation of the Number of Zeros of Linear Combinations of Certain Zeta-Functions”. Lietuvos Matematikos Rinkinys, vol. 38, no. II, Dec. 1998, pp. 43–48 , https://doi.org/10.15388/LMD.1998.37693.