[hackers] [libzahl] Minor text fix || Mattias Andrée

[git]

commit c9c9a5b8fe7cdde58d2e3b6b21332c4cbd32b9b3
Author:     Mattias Andrée <maand...@kth.se>
AuthorDate: Fri Jul 29 00:30:58 2016 +0200
Commit:     Mattias Andrée <maand...@kth.se>
CommitDate: Fri Jul 29 00:30:58 2016 +0200

    Minor text fix
    
    Signed-off-by: Mattias Andrée <maand...@kth.se>

diff --git a/doc/exercises.tex b/doc/exercises.tex
index 14123d2..01dfb39 100644
--- a/doc/exercises.tex
+++ b/doc/exercises.tex
@@ -266,7 +266,7 @@ formula is
     \left ( 1 - \frac{1}{p} \right ).
 }\)
 
-Note that, $\varphi(-n) = \varphi(n)$, $\varphi(0) = 0$,
+Note that $\varphi(-n) = \varphi(n)$, $\varphi(0) = 0$,
 and $\varphi(1) = 1$.