I just found it, also due to Roger Hui.
But this seems missing in JPhrase or wiki's essay on permutation.
NB. v All permutation of y. (Hui)
perm=: [EMAIL PROTECTED] A. i.
NB. v All permutation of x. from y. (Hui)
permc=: ([: ,/ [EMAIL PROTECTED] {"2 1 comb) f.
3 permc 5
0 1 2
0 2 1
1 0 2
1 2 0
2 0 1
2 1 0
0 1 3
0 3 1
1 0 3
1 3 0
3 0 1
3 1 0
0 1 4
0 4 1
1 0 4
1 4 0
4 0 1
4 1 0
0 2 3
0 3 2
2 0 3
2 3 0
3 0 2
3 2 0
0 2 4
0 4 2
2 0 4
2 4 0
4 0 2
4 2 0
0 3 4
0 4 3
3 0 4
3 4 0
4 0 3
4 3 0
1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1
1 2 4
1 4 2
2 1 4
2 4 1
4 1 2
4 2 1
1 3 4
1 4 3
3 1 4
3 4 1
4 1 3
4 3 1
2 3 4
2 4 3
3 2 4
3 4 2
4 2 3
4 3 2
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