Graffiti Calculus

     In my dreams I am an artist -- a cartoonist, perhaps, or a graffiti artist -- so skilled with lines and curves and so clever that my art gives pleasure AND delivers a punch.
     And so I am gratefully into the math-art connections provoked by a new book by Mary-Sherman Willis -- aptly titled Graffiti Calculus (CW Books, 2013).  I first met Willis in December, at Cafe Muse (where I will read next Monday, Feb 3 with Stephanie Strickland) and it was my pleasure also to hear her read again from that collection at the Joint Mathematics Meetings.  These poems by Willis give us, in sixty poetic chapters, the story of a mother seeking her son by following his graffiti tags through the city.  Here is a sample, sections 5 and 6: 

5.
Calculus, Latin for pebble, a chip off the old block tumbled over
               time and distance.
On the gridded sidewalk each step is an integer.  Step on a crack, 
               bread your mother's back.  Step,
drop a pebble.  Step, here was the calculus of you moving away
               from me, each of us an entity, yet linked.
Here was your motion and rate of change, and here my continuity,
               and this my paradox:
if every step I took brought me halfway to you, how many steps
               must I take to reach you?
What was my limit, where we converged as a function of time?
               The textbook says, for any fixed
standard of accuracy, you can always be sure to be within that limit,
               provided you have gone far enough.

6.
The height of a child as he grows over time is a continuous function.
               It was I, the notcher and the dater
on the doorframe through which you cane and went; I the datakeeper,
               demonstrator (see how tall?)
for whom the top notch would become a reach, a stretch; I through
               whom you came, then went,
who built my back and biceps lifting you, tickled I'm coming to get you!
               I developed a taste for a burden,
for your arms ever-reaching.  Now my arms looped your waist,
               your chin on my head.
I was reduced to beck and call at the door. The graph of a continuous
               function can be drawn
without lifting the chalk from the board.  Did you think that you
               and I were through?