1 files changed, 6 insertions, 0 deletions
diff --git a/library/cardinal.tex b/library/cardinal.tex
index d0dec59..8691b30 100644
--- a/library/cardinal.tex
+++ b/library/cardinal.tex
@@ -3,6 +3,7 @@
 \import{set.tex}
 \import{ordinal.tex}
 \import{function.tex}
+\import{numbers.tex}
 
 \begin{definition}\label{finite}
     $X$ is finite iff there exists a natural number $k$ such that
@@ -12,3 +13,8 @@
 \begin{abbreviation}\label{infinite}
     $X$ is infinite iff $X$ is not finite.
 \end{abbreviation}
+
+\begin{definition}\label{cardinality}
+    $X$ has cardinality $k$ iff $k$ is a natural number and 
+    there exists a bijection from $k$ to $X$.
+\end{definition}