Some inference produce terms with large useless redexes such as
(prod.fst (prod.mk _ _)). Since we do normalization during
preprocessing, we can avoid ever even looking at these terms.
We also removed the notation (♯tac) since it is not needed anymore.
@gebner, the comment at elaborator.cpp explains why you had to use the ♯
notation. The workaround is a little bit hackish, but I think it is
worth it. We will use monad lifts in many different places.
