TAOCP 2.3 Exercise 18
In List (3), the notation `L[i_1, i_2, \dots]` refers to the node reached by starting at the root of `L`, following the $i_1$-th child, then the $i_2$-th child of that node, and so on.
Exercise 18. [**] [08] In List (3), what is L[5,1,1]? What is L[3,1]?
Verified: no
Solve time: 26s
In List (3), the notation L[i_1, i_2, \dots] refers to the node reached by starting at the root of L, following the $i_1$-th child, then the $i_2$-th child of that node, and so on. By inspecting List (3), the node L[5,1,1] is obtained by taking the 5th child of the root, then its 1st child, then that node's 1st child. This node corresponds to the element d in the list structure. Similarly, L[3,1] is the 1st child of the 3rd child of the root, which corresponds to the element b.
Hence we have
$\boxed{L[5,1,1] = d, \quad L[3,1] = b}.$