Something for nothing

     Among my favorite mathematical ideas are the seeming-paradoxes -- notions that require a twist and a turn and a leap before one can say "aha."  Using a symbol for "nothing" is one of those leap-requiring ideas.  I don't remember when I first understood zero, but I have enjoyed watching my children -- and now grandchildren -- grapple with ideas of things that are absent rather than present. 
     Here, from Hailey Leithauser, is a poem  that celebrates the cipher.