A Universe of Sorts

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.

§ Mnemonic for Why eta Is Unit: