working on dealing with sets as possible return value of h1d1, to allow for generation to yield successes more frequently.
add *throw-exception-if-failed-to-add-path*
add global variable *throw-exception-if-failed-to-add-complement*
allow child1 and child2 input params to be vectors (convert to sets and re-call)
more work on random generation - trying to understand why [s pronoun verb] and [np det noun] can be generated, but [s [np det noun] verb] sentences can't be generated.