## Cesi's Substitution

### Info

The substitution system uses 4 letters. With:

`$x = \frac{\pi}{7}$`

, `$c = \cos(x)$`

and `$s = \sin(x)$`

They are: two squares of side lengths `$1$`

and `$2-c-s$`

; a rectangle with sides `$c+s$`

and `$2-c-s$`

: and a right triangle with legs `$c$`

and `$s$`

.
The substitution is indicated in the figure. Up to our knowledge, this was the first example of a substitution where the tiles occur in infinitely many orientations.
Obviously, the substitution is not primitive.

Important: The substitution must be started with the large square to get anything interesting.

### Substitution Rule

### Patch