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