From 85465273079c56b420a1cbd710ebf1d8b9c742db Mon Sep 17 00:00:00 2001 From: marcbezem Date: Thu, 5 Sep 2024 10:10:15 +0200 Subject: [PATCH] trival group Aut_Prop(True) --- group.tex | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) mode change 100644 => 100755 group.tex diff --git a/group.tex b/group.tex old mode 100644 new mode 100755 index 45c4810..74a4ecc --- a/group.tex +++ b/group.tex @@ -428,11 +428,11 @@ \subsection{First examples} \begin{enumerate} \item\label{ex:trivgroup} Recall that $\true$, and hence $\true \eqto \true$, is contractible. - Hence $\Aut_{\Set}(\true)$ is a group called the + Hence $\Aut_\Prop(\true)$ is a group called the \emph{trivial group}. \index{trivial group} In fact, for any proposition $P$ we can also identify the trivial group - with $\Aut_{\Set}(P)$, see \cref{xca:group-example-details}. - Unlike $\Set$, the type $\true$ is connected, + with $\Aut_\Prop(P)$, see \cref{xca:group-example-details}. + Unlike $\Prop$, the type $\true$ is connected, so we can also identify the trivial group with $\mkgroup (\true,\triv)$, or with $\mkgroup (C,c)$ for any contractible type $C$ and element $c:C$, or @@ -442,10 +442,10 @@ \subsection{First examples} Recall from \cref{sec:universes} the chain of universes $\UU_0 : \UU_1 : \UU_2 : \dots$ such that for each $i$ all types in $\UU_i$ are also in $\UU_j$ for all $j>i$. -Let $\Set_0$ be the type of sets in $\UU_0$, -\ie $\Set_0\defeq \sum_{S:\UU_0}\isset(S)$. Then $\true:\Set_0$ -and $\Set_0 : \UU_1$ (because the sum is taken over $\UU_0$). -In order to accommodate the trivial group $\Aut_{\Set_0}(\true)$, +Let $\Prop_0 \defeq \sum_{P:\UU_0}\isprop(P)$ be the type of +propositions in $\UU_0$. Then $\true:\Prop_0$ +and $\Prop_0 : \UU_1$ (because the sum is taken over $\UU_0$). +In order to accommodate the trivial group $\Aut_{\Prop_0}(\true)$, the universe ``$\UU$'' appearing as a subscript of the first $\Sigma$-type in \cref{def:pt-conn-groupoid}, reappearing later in \cref{def:typegroup} of the type of groups, @@ -515,7 +515,7 @@ \subsection{First examples} \begin{xca} \label{xca:group-example-details} - Show that $\Aut_{\Set}(P)$ is a trivial group for any proposition $P$. + Show that $\Aut_\Prop(P)$ is a trivial group for any proposition $P$. Verify that $\SG_0$, $\SG_1$, and $\SG_\false$ are all trivial groups. Using~\cref{def:finiteset}, give identifications of type $\Aut_\FinSet(\bn{n})\eqto\Sigma_{\bn{n}}$ for $n:\NN$.