diff --git a/Chapters/chapter6.tex b/Chapters/chapter6.tex
index 4c6b34a..27c9339 100644
--- a/Chapters/chapter6.tex
+++ b/Chapters/chapter6.tex
@@ -993,7 +993,7 @@ \section{Systems of linear differential equations}
 \ldots, c_k$?
 
 There is a theorem in differential equations that says that given an
-initial condition $\xx_0$ there is one and only one solution of
+initial condition $\yy_0$ there is one and only one solution of
 $\yy' = A\yy$ satisfying $\yy(0)=\yy_0$.  So our theoretical question
 above is equivalent to the following quite practical question. Given
 an initial vector $\yy_0$, does there exist a solution $\yy(t)$ of the