Zeros of the extended Selberg class zeta-functions and of their derivative

Levinson and Montgomery proved that the Riemann zeta-function $\zeta(s)$ and its derivative have approximately the same number of non-real zeros left of the critical line. R. Spira showed that $\zeta'\bigl(\tfrac{1}{2}+it\bigr)=0$ implies $\zeta\bigl(\tfrac{1}{2}+it\bigr)=0$. We obtain that in small areas located to the left of the critical line and near it the functions $\zeta(s)$ and $\zeta'(s)$ have the same number of zeros. Actually the result is true for more general zeta-functions from the extended Selberg class $S$. We also consider zero trajectories of a certain family of zeta-functions from $S$.

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