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-rw-r--r--library/set.tex19
1 files changed, 8 insertions, 11 deletions
diff --git a/library/set.tex b/library/set.tex
index 33e5af4..2fd18ea 100644
--- a/library/set.tex
+++ b/library/set.tex
@@ -131,8 +131,7 @@ which applies it to goals of the form “$A = B$” and “$A \neq B$”.
If $x$ and $y$ are empty, then $x = y$.
\end{proposition}
-\begin{proposition}%
-\label{emptyset_subseteq}
+\begin{proposition}\label{emptyset_subseteq}
For all $a$ we have $\emptyset \subseteq a$.
% LATER $\emptyset$ is a subset of every set.
\end{proposition}
@@ -266,8 +265,7 @@ The $\operatorname{\textsf{cons}}$ operation is determined by the following axio
There exists $B\in C$ such that $A\in B$.
\end{proof}
-\begin{proposition}%
-\label{unions_emptyset}
+\begin{proposition}\label{unions_emptyset}
$\unions{\emptyset} = \emptyset$.
\end{proposition}
@@ -553,13 +551,7 @@ The $\operatorname{\textsf{cons}}$ operation is determined by the following axio
Follows by set extensionality.
\end{proof}
-\begin{proposition}%
-\label{inter_subseteq}
- $A\inter B\subseteq A$.
-\end{proposition}
-
-\begin{proposition}%
-\label{inter_emptyset}
+\begin{proposition}\label{inter_emptyset}
$A\inter\emptyset = \emptyset$.
\end{proposition}
\begin{proof}
@@ -620,6 +612,11 @@ The $\operatorname{\textsf{cons}}$ operation is determined by the following axio
Follows by set extensionality.
\end{proof}
+\begin{proposition}\label{inter_subseteq}
+ Suppose $A,B\subseteq C$.
+ Then $A\inter B\subseteq C$.
+\end{proposition}
+
\begin{abbreviation}\label{closedunderinter}
$T$ is closed under binary intersections
iff for every $U,V\in T$ we have $U\inter V\in T$.