ltsgraph shows the Terminate action instead of showing states with a `tick` as done in the book

[mlaveaux]

This might be confusing for users that are following the book.

[mlaveaux]

During the mCRL2 meeting it was deciding that this is basically not super relevant. It might have been useful to have Terminate be a reserved action that perhaps could be overwritten by a flag during linearisation, but as it stands we are not going to doing anything with it.