Living cell masking

[KoKuToru]

The description and the 'A single update step of the model.'-illustration doesn't match.

alive = max_pool(state_grid[:, :, 3], (3,3)) > 0.1
state_grid = state_grid * cast(alive, float32)

But the collab notebook (and the illustration):

pre_life_mask = get_living_mask(x)

.. update state ...

post_life_mask = get_living_mask(x)
life_mask = pre_life_mask & post_life_mask
return x * tf.cast(life_mask, tf.float32)

In the colab notebook, cells are only living if they were living and are living after the update ?

What is the reason behind this modified life_mask ?