[Dune] reminder

[Andreas Dedner]

Hi,
during the summer school two questions arose:
1) Oliver asked about uniqueness of ids:
     I have been wondering about the precise semantics of ids.  In
     particular,  can two entities in the same grid, but with different
     codimensions, have the same id?
     - the gridpaper (part I) says they can
     - The file http://www.dune-project.org/doc/devel/indexidsets.html
       says they cannot
     - both the grid howto and the class documentation do not say
       anything about this
     - UGGrid allows entities with different codimensions to have the
       same id.
     Is this a bug?
2) Can ids be reused during the grid modification, i.e., can a new
    entity have the id of a vanished entity?

We think that
1) ids should be unique through all codimensions
2) ids can be reused during one grid change

Whats the general opinion?
Greetings
Andreas