biblatex > two bibliographies

[Wolfgang Engelmann]

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 might need to use the way Herbert recommended:
define keys in the bib-data file to get different bibliographies, e.g. 
for one entry data:
@{book,
   keywords = {second},
   author =....
}
Can this be done in the options box of the Biblatex Generated 
Bibliography in LyX? I must play with it (with [xxx]??). It is not well 
described in the LyX help file.

I also tried to use two Biblatex Generated Bibliography behind each 
other. The first one contains the bibliography of all the references 
(AUX2.bib). The second one contains only the recommended literature, 
which are in another bib file (AUX3.bib). The pdf output does not show 
any references.

Would be nice to have an example file in LyX which explains -shows the 
way of getting two biblatex Bibiographies.

Wolfgang