Can someone please explain this to me?

As far as my knowledge goes, the following tree

represents a possible implementation of the tree

posted by the author. Node /1/1/2/ has been

added since the author specified an incomplete

tree (as he used "etc.")

1

/ 1 2

/ 2 3

This should totally invalidate the proposed answer,

since "2 "(left side) is not in the same subtree tree

as "2" (right side).

Or did I miss something?

Thanks!