In particular, make sure we always try eassumption before reflexivity.

That range includes tabs and new lines.

Thanks Morten for spotting this problem.

This way we can use set_solver to solve goals involving ∈.

This has bothered me repeatedly in proofs, now I finally got around to fix it at the source

(These instances are not defined for any FinMap to avoid overlapping
instances for EqDecision, which may have awkward consequences for
type class search).

Having Is_true as a type class caused problems with rewrite: when the
rewrited lemma has a premise of the shape Is_true, the rewrite tactic
will complain that it cannot find a type class instance, instead
of generating a goal for that premise.

This also solves a name clash with the extension order of CMRAs.