Free vs Constraints -- Sandburg - Frost

One of the delights of investigation -- in library books or on the internet or walking about in the world -- is that one bit of information opens doors to lots of others.  And so, as I was learning about Eleanor Graham for Monday's posting, I found her essay entitled "The first time I saw Carl Sandburg he didn't see me" and was reminded in a new way of the ongoing debate about the value of formal constraints in poetry.