Fix errors in the manual (most of them found by Ivan Zuboff)

Signed-off-by: Mattias Andrée <maandree@kth.se>

1 files changed, 1 insertions, 1 deletions

diff --git a/doc/exercises.tex b/doc/exercises.tex
index 3a9df19..9a18b99 100644
--- a/doc/exercises.tex
+++ b/doc/exercises.tex
@@ -596,7 +596,7 @@ ptest_llt(z_t n)
 
 $M_n$ is composite if $n$ is composite, therefore,
 if you do not expect prime-only values on $n$, the
-performance can be improve by using some other
+performance can be improved by using some other
 primality test (or this same test if $n$ is a
 Mersenne number) to first check that $n$ is prime.