[mizar] Maintenance

[Andrzej Trybulec <trybulec@math.uwb.edu.pl>]

The life will be a bit easier, if we assign proper subjects to messages,
and try to avoid messages devoted to two different topics. I appreciate
the valuable contribution of Josef on 'Global choice', but why the
subject is 'structures'?
Similarly the last messages related to 'Lexical integrity' are marked
just 'Puzzle', that is justified only in the case of the first message,
maybe.

I do promise to mark my messages properly, or al least to try to do it.

Regards,
Andrzej