I need your help on something. I have a list in input:

```
(1 ((2 3) (4 ((5) (6)))) ((7 8) (9 10)) 11)
```

I want to receive in output the following:

```
((1 2 3 7 8 11)
(1 2 3 9 10 11)
(1 4 5 7 8 11)
(1 4 5 9 10 11)
(1 4 6 7 8 11)
(1 4 6 9 10 11))
```

The functions such as mapcar, mapcan, maplist... do not help. I think that it is necessary to use recursive function, but do not have any idea how.

Answer:

The function you described seems to be DNF calculation. Here is my solution:

```
(defun dnf (f)
(when f
(if (consp f)
(let ((f-car-dnf (dnf (car f)))
(f-cdr-dnf (dnf (cdr f))))
(if (or (null f-cdr-dnf) (every #'consp f))
(append f-car-dnf f-cdr-dnf)
(mapcan
(lambda (f-cdr-cj)
(mapcar (lambda (f-car-cj) (append f-car-cj f-cdr-cj))
f-car-dnf))
f-cdr-dnf)))
`((,f)))))
```

Is it an intern task?

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