[I thought I had sent this message after Mike's first, but apparently
forgot to "Send"]

Hauke,
I could not figure out your approach.

Mike,
I think your solution is correct.
I tested it with the following approach.
First I went to NuVoc and looked up A. to find the following line of code.
   n=: !N=: 4       NB. number of distinct permutations on N=4 points
I then executed the following line which gave me the 26 permutations of
both i.4 and of 0 1 1 0.
   ((i.n) A. i. N);(i.n) A. 0 1 1 0

From there in my editor I manually deleted the offending cases, leaving
only the 8 below. Which I think correspond to your 8.
┌───────┬───────┐
│0 1 3 2│0 1 0 1│
│0 2 3 1│0 1 0 1│
│1 0 2 3│1 0 1 0│
│1 3 2 0│1 0 1 0│
│2 0 1 3│1 0 1 0│
│2 3 1 0│1 0 1 0│
│3 1 0 2│0 1 0 1│
│3 2 0 1│0 1 0 1│
└───────┴───────┘

On Mon, May 25, 2020 at 8:15 AM 'Mike Day' via Programming <
programm...@jsoftware.com> wrote:

> I think there are 8 solutions.
> Given one, minimal, solution,  0 1 3 2, how about this?
>
>    NN((,|."1)@:(|."0 1~i.@#))'0132'
> 0132
> 1320
> 3201
> 2013
> 2310
> 0231
> 1023
> 3102
>
> Any use?
>
> Mike
>
> Sent from my iPad
>
>
>
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