[Oberon] Module aliases - what is the correct way to handle them

[Paul Reed]

Hi Jörg,

> IMPORT Y := M0, M0;
> Why should this be forbidden?
> In Oberon it‘s absolutely fine to have the same object visible under
> different names...

Thanks, I see what you mean.  But now I'm thinking: extending your 
argument, would it not then also be valid to have the same module 
available under multiple aliases, not just one, e.g.


   IMPORT Y := M0, M0, X := M0;

So we need clear and hopefully simple code which prevents an import 
twice, by checking canonical (org-)names, but then checks for 
inadvertent multiple definitions of aliases - where a non-aliased module 
has its canonical name as its alias.  Or maybe the other way around.

Yikes.  I get it now - hmm.  Thanks again!

Cheers,
Paul