Is this a problem from my side or it’s a general problem?
The next cell after the hash_value_of_vector function
Tried running the entire notebook again and still
It worked for me. Perhaps you accidentally modified the cell right before the hash_value_of_vector cell that defines planes_l:
That cell was just given to you and did not require any changes. If you would like to get a clean copy of the notebook either to compare with or to use as a basis for starting again (just copying over your code from the “YOUR CODE HERE” sections), here is a thread about how to do that.