return [ rec(
      invers := ( 1, 3)( 2, 8)( 4,11)( 5, 9)( 6,10)( 7,12),
      nbP := 12,
      next := ( 1, 2)( 3, 4, 5)( 6, 7, 8, 9)(10,11,12) ) ];
