Drop `DiagNone` precondition of `lookup_merge` rule of `FinMap` interface.
This fixes issue #94 (closed)
- Drop
DiagNone
class. - Add
merge_proper
instance. - Simplify lemmas about
merge
by dropping theDiagNone
precondition. - Generalize lemmas
partial_alter_merge
,partial_alter_merge_l
, andpartial_alter_merge_r
. - Drop unused
merge_assoc'
instance, which seems unused, and seems pointless to generalize.