\newcommand{\xrdefn}[1]{\ref{\forcsvlist{\xrdefnhelper}{#1}}}
\newcommand{\hrdefn}[2][]{\ifstrempty{#1}{\hyperref[defn:#2]{#2}[\ref{defn:#2}]}
{\hyperref[defn:#1]{#2}[\ref{defn:#1}]}}
+
+\newcommand\xrexhelper[1]{ex:#1}
+\newcommand{\xrex}[1]{EX: \ref{\forcsvlist{\xrexhelper}{#1}}}
+
\begin{document}
%>>>
% Intro <<<
%
$C$ is a \defn{coseparator} if $\forall_{f,g : B \to A} f \ne g
\Rightarrow \exists_{h : A \to C} . h \circ f \ne h \circ g$. (\S7.17)
- (Contrast monomorphism.)
+ (Contrast \hrdefn{monomorphism}.)
% \paragraph{}
% %
%
$S$ is a \defn{separator} if $\forall_{f,g : A \to B} f \ne g
\Rightarrow \exists_{h : S \to A} . f \circ h \ne g \circ h$. (\S7.10)
- (Contrast epimorphism.)
+ (Contrast \hrdefn{epimorphism}.)
$S$ is a separator iff $\mbox{hom}(S,-)$ is faithful. (\S7.12)
\paragraph{}
\paragraph{}
%
An object that is both initial and terminal is called a \defn{zero}.
- (\S7.7)
+ (\S7.7) \xrex{mon0}
% >>>
\section{Arrow Properties} % <<<
Z & Q \ar@{..>}[l]^u & B \ar[l]^q \ar@/^1pc/[ll]^{z} & A \ar@<1ex>[l]^f \ar@<-1ex>[l]_g
}\]
Coequalizers are essentially unique (\S7.70.1) and epic (\S7.71,\S7.75.2).
+ \xrex{setcoeq}
\paragraph{}
%
\[\xymatrix{\forall_{i,j} ie = je \Rightarrow i = j & A \ar@{->>}[r]^e & B \ar@<1ex>[r]^{i} \ar@<-1ex>[r]_j & C} \]
%
If $f$ and $g$ are epis, then so is $g \circ f$; if $g \circ f$ is epi,
- then so is $g$. (\S7.41)
+ then so is $g$. (\S7.41) \xrex{setmonepi}
\paragraph{}
%
Z \ar@{..>}[r]^u \ar@/_1pc/[rr]^{z} & E \ar[r]^e & A \ar@<1ex>[r]^f \ar@<-1ex>[r]_g & B \\
}\]
Equalizers are essentially unique (\S7.53) and monic (\S7.56,\S7.59.2).
+ \xrex{seteq}
\paragraph{}
%
\[\xymatrix{\forall_{i,j} mi = mj \Rightarrow i = j & C \ar@<1ex>[r]^{i} \ar@<-1ex>[r]_j & A \ar@{{ >}->}[r]^m & B} \]
If $f$ and $g$ are monos, then so is $g \circ f$; if $g \circ f$ is mono,
then so is $f$. (\S7.34) Objects with monomorphisms to $X$ are called
- \defn{subobjects} of $X$ (Awodey:D5.1).
+ \defn{subobjects} of $X$ (Awodey:D5.1). \xrex{setmonepi}
\paragraph{}
%
- A \defn{point} (Awodey:p32) of $C$ is any $c : 1 \to C$.
+ A \defn{point} (Awodey:p32) of $C$ is any $c : 1 \to C$. \xrex{monpt}
\paragraph{}
%
%
Several morphism properties combine in useful ways:
\begin{itemize}
- \item mono, epi $\Rightarrow$ \defn{bimorphism} (\S7.49)
+ \item mono, epi $\Rightarrow$ \defn{bimorphism} (\S7.49) \xrex{monbi}
\item section $\Rightarrow$ regular mono (\S7.35, \S7.59.1)
\item regular mono $\Rightarrow$ extremal mono (\S7.59.2, \S7.63)
\item retraction $\Rightarrow$ epi (\S7.42)
% >>>
\section{Adjoints and Adjoint Situations} % <<<
+\label{sec:adj}
+
+Be sure to see \autoref{sec:adjex} for examples.
\subsection{Joy Approach}
\subsection{$\mathbf{Set}$}
- \paragraph{} Epic is surjective, monic is injective.
+ \paragraph{}\label{ex:setmonepi}
+ %
+ \hrdefn[epic]{Epic} is surjective, \hrdefn{monic} is injective.
- \paragraph{}
- Coequalizers correspond to equivalence classes (\S7.69.1): Let $\sim$ be
- {\em the smallest} eq. rel. s.t. $\forall_{a \in A} f(a) \sim g(a)$;
- then $(Q,q) = (B/\sim, b \mapsto \brak{b}_\sim)$ is a coequalizer of $f$
- and $g$.
+ \paragraph{}\label{ex:setcoeq}
+ %
+ \hrdefn[coequalizer]{Coequalizers} correspond to equivalence classes
+ (\S7.69.1): Let $\sim$ be {\em the smallest} eq. rel. s.t. $\forall_{a \in
+ A} f(a) \sim g(a)$; then $(Q,q) = (B/\sim, b \mapsto \brak{b}_\sim)$ is a
+ coequalizer of $f$ and $g$.
- \paragraph{}
- Equalizers: $(E,e) = (\set{x \mid f(x) = g(x)} \subseteq X, \subseteq)$.
+ \paragraph{}\label{ex:seteq}
+ %
+ \hrdefn[equalizer]{Equalizers}: $(E,e) = (\set{x \mid f(x) = g(x)} \subseteq X, \subseteq)$.
\subsection{$\mathbf{Mon}$}
- \paragraph{}
+ \paragraph{}\label{ex:monbi}
%
\hrdefn[bimorphism]{Bimorphisms} are not isos: ($(\mathbf{N},+,0) \to
(\mathbf{Z},+,0)$). (Pierce:\S1.6.3)
- \paragraph{}
+ \paragraph{}\label{ex:mon0}
%
- $(\set{*},\cdot,*)$ is a (the) zero.
+ $(\set{*},\cdot,*)$ is a (the) \hrdefn{zero}.
- \paragraph{}
+ \paragraph{}\label{ex:monpt}
%
- Each monoid $M$ has only one point, $1 \to M$.
+ Each monoid $M$ has only one \hrdefn{point}, $1 \to M$.
\subsection{Adjoint Situations and Monads}
+ \label{sec:adjex}
+ Defintitons in \autoref{sec:adj}.
\paragraph{}
%