It is the first example on page 72, the one with the highlighting.
[ 1 | [ 2 | [ 3 | [] ] ]
Needs to be changed to:
[ 1 | [ 2 | [ 3 | [] ] ] ]
4 opening square brackets and 4 closing square brackets.
Two rows down, there is a working example so hopefully, people have been using that to actually copy/paste the example, but I was trying to understand the recursive list structure and this tripped me up for a moment before I realized what is going on.