docs: def merge_Fm(dfs_data):
      """Merges Fm-1 and Fm, as defined on page 19 of the paper."""
      FG = dfs_data['FG']
      m = FG['m']
      FGm = FG[m]
      FGm1 = FG[m-1]
  
      if FGm[0]['u'] < FGm1[0]['u']:
          FGm1[0]['u'] = FGm[0]['u']
  
      if FGm[0]['v'] > FGm1[0]['v']:
          FGm1[0]['v'] = FGm[0]['v']
  
      if FGm[1]['x'] < FGm1[1]['x']:
          FGm1[1]['x'] = FGm[1]['x']
  
      if FGm[1]['y'] > FGm1[1]['y']:
          FGm1[1]['y'] = FGm[1]['y']
  
      del FG[m]
      FG['m'] -= 1