.

I'm not sure what you mean? Can you provide an example?

This should be len(greeting) - 1, but it can be omitted anyway, as [1:] will substring from the second element to the last.

Edited, see if now it is fine for you :)

thanks, changed pre-set code to match what the test expects.

It would be nice to have some pre-set test to start from.

There'a typo in pre-set code, the method is named post_postorder, but the tests expect tree_to_postorder_list.

wrong function name for post-order traversal

I don't think that's necessary.

What are the solutions if 6 words together appear? Should it be the 6 different ways of choosing 5 of the words, or just the 6 words?

The description is difficult to understand