Hi Kasper,
I tried doing a complete uninstall/reinstall. I uninstalled both Cadabra and Cadabra2 and manually purged any libraries, configuration files, and other files and directories I could find related to either Cadabra or Cadabra2.
Now that Cadabra2 is in the Mint repository, I think I eventually installed it from there.
I can open cadabra2-gtk and at first sight it appears to work, but any line terminated with a ; causes it to crash with the following error:
"symbol lookup error: cadabra2-gtk: undefined symbol: _ZN13exec_stream_t5startERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEES7_"
For example, if I input just the line
{a,b}::Indices(position=fixed).
it executes without a problem, but if I input
{a,b}::Indices(position=fixed);
it crashes with the above error. Likewise if I enter
{a,b}::Indices(position=fixed).
A_{a}^{b};
it again crashes with the same error. If I do the same thing in a terminal I get the following error
File "<console>", line 1
A_{a}^{b};
^
SyntaxError: invalid syntax
Maybe I should try the complete uninstall/reinstall again, but I'm beginning to worry that I'm messing up my system because I'm starting to get other weird system behaviours, like my camera randomly crashes during Skype calls.