Help!  I got myself in a mess after updating.  The usual, reverting to lightdm 
and LXDE.  Which mess I made worse.  Well, I couldn't really see what I was 
doing.  So I purged lightdm.  No better.  So I purged LXDE.  No better.  So I 
purged then installed TDE.  

aptitude purge tde-trinity
aptitude install tde-trinity
(The second as per 
https://wiki.trinitydesktop.org/Debian_Trinity_Repository_Installation_Instructions )

Nothing much happened.  Only one package was touched.

<aptitude show> says that **LXDE is not installed** and that TDE is installed.  
It says that lightdm is not installed.  It says that tdm-trinity is 
installed.

But when I boot up it is LXDE that launches, bypassing any dm.  Yes, I know.  
That sounds totally mad.  But I have repeatedly checked.  I am flummoxed.

Reporting real error messages is terribly difficult because I haven't got LXDE 
set up so that I can see it well, and the virtual terminals are impossible.

Wiping and reinstalling would be the easiest thing to do, and also the 
quickest.  But it would also be defeatist.  Has anyone any other ideas?

Thanks,
Lisi