In the following diagram, it is not possible to drag Y on to the end of the arrow, despite it being empty.

In such a situation, it makes sense to allow Y to be dragged on top of the empty node.

Pretty-print GATs as LaTeX in both of the following styles:

1. Cartmell-style linear notation

2. natural-deduction-style tree notation
   <img width="680" alt="image" src="https://user-images.githubusercontent.com/316610/91097121-f953b080-e613-11ea-8dda-8da598

Do you intend to implement some of the functions Scott Wlaschin has in its AsyncResult/Result modules, e.g.

AsyncResult.catch
AsyncResult.ofAsync
AsyncResult.ofSuccess
AsyncResult.ofError
AsyncResult.ofResult?

https://github.com/swlaschin/DomainModelingMadeFunctional/blob/master/src/OrderTakingEvolved/Result.fs

Complete algorithm: http://web.cecs.pdx.edu/~mpj/pubs/polyrec.html

We can already draw arbitrary permutations as sequences of swaps, but this can clutter diagrams unnecessarily.
An easy fix is to define Permutation boxes, with an appropriate refactoring of the drawing module.

These could then be constructed by calling diagram.permute as proposed in issue oxford-quantum-group/discopy#17.

One design decision that needs to be tak

• untabify
• indent
• align where needed