The build fails with the following error.

 cmake: /usr/lib/libc.so.6: version `GLIBC_2.34' not found (required by /usr/lib/libstdc++.so.6)
 cmake: /usr/lib/libc.so.6: version `GLIBC_2.34' not found (required by /usr/lib/libgcc_s.so.1)

It turned out, the system was in inconsistent state -- some of the
packages were not updated. And now, when new glibc reached the repos, it
broke the system....

also makes protected fields private

which is in a next step promoted again...

Closes #205

Closes #215