This better seals off their definition. Although it did not give
much of a speedup, I think it is conceptually nicer.

I am now also using reification to obtain the indexes corresponding to
the stuff we want to cancel instead of relying on matching using Ltac.

With Set Printing All, these notations make me loose overview entirely.

barrier: strive for consistency between barrierGF and the inGF assumptions; also change some instance names