Following the answer of this question I tried to run the code proposed by Mark in the third "code window". What I obtain is:
I can't find file `tikzlibrarymath.code.tex'
Runninig the terminal command
tlmgr update --all
I obtain the following
(running on Debian, switching to user mode!) tlmgr: package repository http://ctan.mirror.garr.it/mirrors/CTAN/systems/texlive/tlnet tlmgr: no updates available
So I suppose that my packages are updated. The question is: how to install properly the tikz library math? In order to install it in a local dir, I have (partially) followed the answer to this question , but now I'm not able to find the repositories and the proper Tex Directory Structure.