In [lecture 2](https://www.youtube.com/watch?v=jm3bJrULMqM) (about time 5:30), Brendan introduces a notion of **Shape**.
I like this idea. Each Shape (object, pair, arrow, isomorphism) suggests _the essence of_ a basic idea in Category Theory.
An essence is not formally defined. I can play with it in my own way, with tools I'm familiar with.
This is roughly the table that Brendan presented.
```
| Shape Label | Essence Of | Objects | Arrows |
| ----------- | ----------- | ------- | ------ |
| 1 | object | 1 | 1 |
| P | pair | 2 | 2 |
| 2 | arrow | 2 | 3 |
| I | isomorphism | 2 | 4 |
```
[Graphviz](https://graphviz.org/), can roughly reproduce what Brendan drew on the blackboard.
A number of online sites can parse Graphviz .dot notation, and display it as a Scalable Vector Graphics (SVG) image.
[WebGraphviz](http://www.webgraphviz.com/) is one such site. Copy any of the following four _digraph_ lines, paste it into the WebGraphviz site, click _Generate Graph!_, and view the SVG image (as shown below).
digraph 1 {x->x; label="1 object";}

digraph P {x->x y->y; label="P pair";}

digraph 2 {x->x->y->y; label="2 arrow";}

digraph I {x->x->y->y->x; label="I isomorphism";}

I wonder what other essences are lurking out there, or is this as far as we can go with this concept?