User blog comment:Hyp cos/tree function and TREE(3)/@comment-5150073-20140624084600/@comment-11227630-20140624092032

In TREE(n) and SCG(n) the "homeomorphical embedding" means different things. We call A is a minor of B if we can operate on B and make it to A as follows.

In SCG(n), there're 3 operations:
 * Delete a 0-degree vertix
 * Delete an edge
 * Contract edges (replace two adjacent vertices with one vertex connected to all of their neighbours)

In TREE(n), there're only 2 operation:
 * Delete a leaf
 * Delete a 1-child vertix and connect its child to its parent

So in TREE(n), () isn't a minor of (()), and [] isn't a minor of [()], but in SCG(n) they are.