code: def _removeSingleMemberGroupReferences(kerning, leftGroups, rightGroups):
      
      new = {}
      for (left, right), value in kerning.items():
          left = leftGroups.get(left, left)
          right = rightGroups.get(right, right)
          new[left, right] = value
      return new
docs: Translate group names into glyph names in pairs
      if the group only contains one glyph.