predecessors

[mikeries]

I found the 'predecessor' properties to be confusing. There wasn't really any explanation of what they are, and they don't appear to have any purpose in the code.

The predecessor seems to be a pointer back the to 'parent' node, and at some iteration of the curriculum it probably made sense, but currently it isn't needed.

I'd be happy to rewrite the lab to remove it if that would be helpful.