$A \in \mathbf{A}$ to $\tau_A : FA \to GA$ s.t.
$\forall_{f : A \to A'} . G f \circ \tau_A = \tau_{A'} \circ F f$. (\S6.1)
+ There is special notation for functors applied to natural transformations
+ and vice-versa (\S6.2): $(F\tau)_A = F(\tau_A)$ and $(\tau F)_A =
+ \tau_{FA}$.
+
All functors \defn{preserve} (in $\mathbf{A}$ implies in $\mathbf{B}$)$\dots$
\begin{itemize}
\item isomorphisms. (\S3.21)
$(\eta,\epsilon) : F \dashv G : \mathbf{A} \to \mathbf{B}$ is a
\defn{adjoint situation} if the above relationships hold. (\S19.7)
- A \defn{monad} on $\mathbf{X}$ is $(T : \mathbf{X} \to \mathbf{X},
- \eta : id_{\mathbf{X}} \natto, \mu : T^2 \natto T)$ s.t.
- \[\xymatrix@R=10pt{
- T^3 \ar[r]^{T\mu} \ar[d]^{\mu T} & T^2 \ar[d]^\mu \\
- T^2 \ar[r]^{\mu} & T
+ A \defn{monad} (\S20.1) on $\mathbf{X}$ is $(T : \mathbf{X} \to \mathbf{X},
+ \eta : id_{\mathbf{X}} \natto T, \mu : T^2 \natto T)$ s.t.
+ \[\forall_X \quad
+ \xymatrix@R=10pt{
+ T^3X \ar[r]^{T(\mu_X)} \ar[d]^{\mu_{TX}} & T^2X \ar[d]^{\mu_{X}} \\
+ T^2X \ar[r]^{\mu_X} & TX
} \quad \xymatrix@R=10pt{
- T \ar[r]^{T\eta} \ar[dr]_{id} & T^2 \ar[d]^\mu & T \ar[l]_{\eta T} \ar[dl]^{id} \\
- & T &
+ TX \ar[r]^{T(\eta_X)} \ar[dr]_{id_{TX}} & T^2X \ar[d]^{\mu_X} & TX \ar[l]_{\eta_{TX}} \ar[dl]^{id_{TX}} \\
+ & TX &
}\]
\end{document}