*Intrinsic Defects, Fluctuations of the Local Shape, and the Photo-Oxidation of Black Phosphorous*. He's the Academic Director of the Epsilon Camp. And, along with Alex Bellos, he's co-authored Patterns of the Universe. So when he says that a square can have wiggly lines and angles of 72 degrees, who am I to argue?

Do you see the square? |

For my morning session at TMC '16, I chose Tessellation Nation. There were several other interesting options, but the temptation of spending 6 hours over 3 days playing in the Triangleman's sandbox, in his Minneapolis backyard, was too hard to resist. We would be given the freedom to explore whatever we wanted, for however long we wanted, with whomever we wanted. All Christopher asked was that we start with a question or goal, no matter how vague or obscure. Fortunately Max went before me, and I adopted his:

*When does play become math?*

I went right for the turtles. |

Elizabeth was interested Escher drawings, and spent time exploring, tracing, and creating designs. |

Bryan and Malke worked with these shapes... |

...and had some questions. Good thing John Golden was around to explain periodic tiling. |

Jose got all 3-D on us. |

Graham worked on hexagons... |

...and so did Henri. "Hexagons will humble you," he said. And he was absolutely correct. |

Max and Malke disappeared for a while. They had an idea and needed more space. |

Edmund Harriss brought along some laser cut shapes for us to explore, and told us that if we put them together we could make a ball. I had seen Edmund present a My Favorite at TMC '15, and knew him as the co-author of the brilliant book

__Patterns of the Universe__. But I hadn't had the chance to meet and get to know him, and the shapes looked cool, so I dropped the turtles and, along with Bryan Anderson, jumped in.

First we had to remove the shapes from the sheet. They could be joined together by tabs. |

That was fun! |

Then he gave us another project to work on. He told us that if we put the shapes together in just the right way, we could create a cool tessellation that would ripple. He explained that, around any vertex, we would need to alternate 2 triangles, a square, another triangle, and then another square.

And that's when I got dizzy.

Because I didn't see any triangles or squares.

And that's when my play became math.

Because I wanted to know what in the world he was talking about.

He pointed out a shape that had 4 wiggly sides:

I tried to imagine the wiggly sides pulled taut to form straight lines that intersected at 90 degree angles. |

**Me:**But Edmund, that's not a square! A square has straight sides and angles of 90 degrees! This shape has wiggly sides and angles of... ?

**Edmund:**72 degrees.

**Me:**But that's not a square!

**Edmund:**Really?

**Me:**Well a square has 4 sides, all the same length, and this shape has 4 sides, all the same length. And a square has 4 vertices and so does this shape. And in a square all the angles are equal, and all the angles in this shape are equal. So maybe it is a square?

**Edmund:**The most important thing I learned getting my Ph.D. was to be flexible. I had to learn how to bend myself around the math. In order for us to talk about what's happening here we are going to call this shape a square.

**Me:**Not for nothing, but it sounds like you're bending the math around yourself! But I'm over it. A square it is!

I felt an exciting sense of liberation. Math, which had always seemed to me to be a rigid, inflexible, no nonsense, no talking back, no coloring outside the lines set of arbitrary and infuriating rules and regulations, suddenly had become, in Edmund's hands, something to play with. In my hands it was lifeless. In Edmund's, it was art. I was finally beginning to understand what all the fuss was about.

Edmund explained that what we would be creating was called a uniform tiling with curvature. He said that to understand what was happening mathematically we would need to use something called

*Differential Geometry*, which is calculus in several dimensions. He said the equations would be quite complex.

I touch calculus. I've never been this close to it, nor ever wanted to be. I'm going to be 55 years old in just a few weeks. I'm ready to learn now. |

Edmund Harriss, right, with Henri Piccioto. Twitter Math Camp, Minneapolis, MN, July 17, 2016. |