## § Mnemonic for why `eta`

is unit:

- Remember that given an adjunction $F \vdash G$, the unit of the adjunction is $\eta: 1 \to GF$.
- We use the symbol
`eta`

because it's `yunit`

, and `eta`

is `y`

in `greek`

(which is why the vim digraph for `eta`

is `C-k y*`

) - $\eta$ is
`unit`

, since when you flip it, you get $\mu$, which is $\mu$-ltiplication (multiplication). Hence $\eta$ is the unit for the multiplication to form a monoidal structure for the monad.