docs: def export_off(vertices, triangles, filename):
      """
      Exports a mesh in the (.off) format.
      """
      
      with open(filename, 'w') as fh:
          fh.write('OFF\n')
          fh.write('{} {} 0\n'.format(len(vertices), len(triangles)))
  
          for v in vertices:
              fh.write("{} {} {}\n".format(*v))
              
          for f in triangles:
              fh.write("3 {} {} {}\n".format(*f))