It seems I still struggle with [the "in" operator in numpy](https://stackoverflow.com/questions/7989676/numpy-need-a-hand-in-understanding-what-happens-with-the-in-operator/7989956#7989956). Here's the situation:

```
>>> a = np.random.randint(1, 10, (2, 2, 3))
>>> a
array([[[9, 8, 8],
        [4, 9, 1]],

       [[6, 6, 3],
        [9, 3, 5]]])

```

I would like to get the indexes of those triplets whose second element is in `(6, 8)`. The way I intuitively tried is:

```
>>> a[:, :, 1] in (6, 8)
ValueError: The truth value of an array with more than one element...

```

**My ultimate goal would be to insert at those positions the the number preceding those multiplied by two.** Using the example above, `a` should become:

```
array([[[9, 18, 8],   #8 @ pos #2 --> replaced by 9 @ pos #1 by 2
        [4, 9, 1]],

       [[6, 12, 3],   #6 @ pos #2 --> replaced by 6 @ pos #1 by 2
        [9, 3, 5]]])

```

Thank you in advance for your advice and time!