Trees as Linked Lists in Common Lisp (2010)

The figure is correct. In the first part of the article, a tree is represented as (cons root children). So the example tree

    (1 (2 6 7 8) 3 (4 (9 12)) (5 10 11))

has "1" at its root, and four children. Its first child

       (2 6 7 8)

is a tree with "2" at its root, and three children which are all leaves. And so on.

The solid lines are parent relationships, and the dotted lines are sibling relationships. For each list, the first two items are connected by a solid line, and the remaining items by dotted lines.