Art Generation with Neural Style Transfer programming assignment > Exercise 2 - gram_matrix is gone

Art Generation with Neural Style Transfer programming assignment > 4.2.1 - Style Matrix and Exercise 2 - gram_matrix parts are gone.

I can’t see the content of 4.2.1 - Style Matrix and Exercise 2 - gram_matrix parts.
I can’t even click and go to the two links (4.2.1 - Style Matrix, Exercise 2 - gram_matrix) in Table of Contents.

I think the contents of these two parts were gone and disappeared.
How to restore them?

There’s a link to refresh your workspace at top of the notebook. Please follow the steps listed there