Inspired by 6 Letter Word Evolution, this is a 4 letter word evolution, which defines a tetragram. It's NOT a decision number evolution! The sequence goes AAAA, AAAB, AAAC, AAAD, AAAE, etc.
CREDIT TO ALL!
![Tetragram Evolution [ AAAB --> AAAC ]](https://cdn2.scratch.mit.edu/get_image/project/349785993_480x360.png)
