Integral of 1/cos(x) in CAS

[parisse]

I did not observe a crash but it runs forever. It's a well known problem that it's sometimes difficult to interrupt a CAS computation on the Prime, because the CAS kernel was designed to run on a desktop OS. The best I can do is to commit a workaround each time a user reports a problem, for example here in geogebra SVN
https://dev.geogebra.org/trac/changeset/49639/