### Existence and reduction of generalized Apostol-Bernoulli, Apostol-Euler and Apostol-Genocchi polynomials

One can find in the mathematical literature many recent papers studying the generalized Apostol-Bernoulli, Apostol-Euler and Apostol-Genocchi polynomials, defined by means of generating functions. In this article we clarify the range of parameters in which these definitions are valid and when they provide essentially different families of polynomials. In particular, we show that, up to multiplicative constants, it is enough to take as the “main family” those given by $${\left(\frac{2}{\lambda {e}^{t}+1}\right)}^{\alpha}{e}^{xt}=\sum _{n=0}^{\infty}{\mathcal{E}}_{n}^{\left(\alpha \right)}(x;\lambda )\frac{{t}^{n}}{n!}\phantom{\rule{0.166667em}{0ex}},\phantom{\rule{2.0em}{0ex}}\lambda \in \u2102\setminus \{-1\}\phantom{\rule{0.166667em}{0ex}},$$ and as an “exceptional family”...