( (
  =
    .   !arg:#:~<0
      &   ( (=.!arg$!arg)
          $ (
            =
              .
                ' (
                  .   !arg:<2
                    |   (($arg)$($arg))$(!arg+-2)
                      + (($arg)$($arg))$(!arg+-1)
                  )
            )
          )
        $ !arg
  )
$ 30
)