code: def enforce_vertical_symmetry(pixmap):
      '''Enforces vertical symmetry of the pixelmap.
      Returns a pixelmap with all pixels mirrored in the middle.
      The initial ones still remain.'''
      mirror = []
      for item in pixmap:
          y = item[0]
          x = item[1]
  
          if x <= IMAGE_APEX:
              diff_x = diff(x, IMAGE_APEX)
              mirror.append((y, x + (2 * diff_x) - 1))
  
          if x > IMAGE_APEX:
              diff_x = diff(x, IMAGE_APEX)
              mirror.append((y, x - (2 * diff_x) - 1))
  
      return mirror + pixmaf enforce_vertical_symmetry(pixmap):
      '''Enforces vertical symmetry of the pixelmap.
      Returns a pixelmap with all pixels mirrored in the middle.
      The initial ones still remain.'''
      mirror = []
      for item in pixmap:
          y = item[0]
          x = item[1]
  
          if x <= IMAGE_APEX:
              diff_x = diff(x, IMAGE_APEX)
              mirror.append((y, x + (2 * diff_x) - 1))
  
          if x > IMAGE_APEX:
              diff_x = diff(x, IMAGE_APEX)
              mirror.append((y, x - (2 * diff_x) - 1))
  
      return mirror + pixmap
docs: Enforces vertical symmetry of the pixelmap.
      Returns a pixelmap with all pixels mirrored in the middle.
      The initial ones still remain.