## Card Shuffling Font |
## by Erik Demaine and Martin Demaine, 2015 |

A **perfect shuffle**
cuts a deck of cards exactly in half, and riffle shuffles them together
with exact alternation between the two halves.
There are two different perfect shuffles depending on which half drops a
card first, placing the top card either on top
(**outside** or **O**) or one card down
(**inside** or **I**).
By an appropriate sequence of perfect shuffles
(just logarithmically many), you can bring any desired card
to the top of the deck; this is known as Elmsley's Problem, which was
solved by Persi Diaconis and Ron Graham.

In this font, we start with a sorted deck of 26 cards labeled A through Z
(shown at the left), and for each letter in the message, apply the
(at most 5!) perfect shuffles needed to bring that letter to the top of
the deck (shown in bold), so that it could be presented to the audience.
The **I**s and **O**s encode the needed shuffles, and the
graphics show how the cards re-order along the way.
This font is unusual in how the encoding of each letter depends on the
current location of the letter in the deck, which in turn depends on the
sequence of letters and resulting shuffles performed before.
The font was prepared in honor of
Ron Graham's
80th birthday.