This week’s topic – occasioned by a recent evening at a Broadway theater  -- is the (often blurry) boundaries of art.  More specifically, it’s the Broadway musical, a genre notorious for sometimes straddling that boundary. The show in question was a production of “Merrily We Roll Along,” with music and lyrics by Stephen Sondheim. The great Stephen Sondheim, whose career began with his lyrics for one of greatest of all musicals, “West Side Story” (1957), with music by Leonard Bernstein. Now that was a work of art.