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