Revert "fix mirror lub equality assertion"
Revert "fix mirror lub equality assertion"

This reverts commit d306a892d853197fbf1a7621227ca5ea4c48db65.

Turns out this is incorrect: https://github.com/mirah/mirah/commit/d306a892d853197fbf1a7621227ca5ea4c48db65#commitcomment-5345748

KeenS/mirah,KeenS/mirah,felixvf/mirah,uujava/mirah,mirah/mirah,felixvf/mirah,felixvf/mirah,mirah/mirah,mirah/mirah,KeenS/mirah,uujava/mirah,felixvf/mirah,mirah/mirah,uujava/mirah,KeenS/mirah,uujava/mirah,uujava/mirah