[isabelle-dev] Duplicate theory??

[Lars Hupel]

> The policy for the AFP has always been in the past: it is ok to fix
> things a few days later. Not sure why this deserves the adjective
> "catastrophic".

"catastrophic" because the failure prevented the *entire AFP* from being 
built, hence the error message.

Maybe Makarius could change that behaviour and instead of "build" 
refusing to build anything, only exclude malformed sessions.