Hi
I am playing around with building graph using 'tying the knote' technique ,
according to rule a is child of b iff predicate a b == true
Additional step is to detect loops in graph to enable it's print . Then I am using graph traversal to detect loops prior to calling show .

For now I am stuck debugging loop detection . I am using 'trace' for a first time and I am not sure I am fully understanding it's behavior
In additional I tried to make all calculations strict for debug .

Can you please provide tips / review code .
 
My code is at
http://pastebin.com/5RvQ42z2

Thanks,
Lev