ex 4.75 - implement "unique"
ex 4.75 - separate file for unique handler
ex 4.75 - done
ex 4.76 - impl stream combine
ex 4.76 - get stuck here. about frame bindings
ex 4.76 - testings on conjunction handler
ex 4.76 - plan
ex 4.76 - potential approach
ex 4.76 - impl merge-frame with some TODO
ex 4.76 - some comments
ex 4.76 - not working yet
ex 4.76 - try implementing unify-match2
ex 4.76 - rearrange args & wrong value fix
ex 4.76 - extend-if-possible
ex 4.76 - depends-on?
ex 4.76 - done

I think this approach is wrong so I'm done with it.
ex 4.77 - some justification
ex 4.77 - done
ex 4.78 - some experiment about amb vs qeval
ex 4.78 - how to do "append" in amb?