[hackers] [libzahl] Fix typo || Mattias Andrée

[git]

commit 9d613b2d3436cf91c9624d0414544e74d49256a6
Author:     Mattias Andrée <maand...@kth.se>
AuthorDate: Thu May 12 01:19:23 2016 +0200
Commit:     Mattias Andrée <maand...@kth.se>
CommitDate: Thu May 12 01:19:23 2016 +0200

    Fix typo
    
    Signed-off-by: Mattias Andrée <maand...@kth.se>

diff --git a/doc/arithmetic.tex b/doc/arithmetic.tex
index 45097e2..efadf17 100644
--- a/doc/arithmetic.tex
+++ b/doc/arithmetic.tex
@@ -195,7 +195,7 @@ This is a natural extension to the observations
 
 \vspace{-1em}
 \[ \hspace*{-0.4cm}
-    \forall n \in \textbf{Z}_{+} \exists B \subset \textbf{Z}_{+} : b = 
\sum_{i \in B} 2^i
+    \forall b \in \textbf{Z}_{+} \exists B \subset \textbf{Z}_{+} : b = 
\sum_{i \in B} 2^i
     ~~~~ \textrm{and} ~~~~
     a^{\sum x} = \prod a^x.
 \]