biblatex > two bibliographies

[Daniel]

On 03/08/2021 18:12, Wolfgang Engelmann wrote:
> Thanks, Daniel and Herbert for the proposals.
> Daniels method works alright, except that it produces Š=Š= at the begin.
> I don't know how to get rid of them.
> 
> Further Readings
> Š=Š=
> Bünning, E. (1983). The physiological clock. 2nd ed. Vol. 1. Heidelberg 
> Science Library. Springer New York.
> Forger, D. B. (2017). Biological clocks, rhythms, and oscillations - The 
> theory of biological timekeeping. MIT Press.

I don't see these symbols in the example file. So, there might be 
problem with the files you are using. But it is hard to tell without a 
minimal example or log file.

Daniel