diff --git a/.gitignore b/.gitignore
index 1f87318..8b72d6f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,4 @@ indent.log
 /node_modules/
 package-lock.json
 /src/session--composition-and-inheritance/resources/*.svg
+/result
diff --git a/src/session--composition-and-inheritance/preamble.tex b/src/session--composition-and-inheritance/preamble.tex
index ce6cf74..966a8ce 100644
--- a/src/session--composition-and-inheritance/preamble.tex
+++ b/src/session--composition-and-inheritance/preamble.tex
@@ -15,7 +15,8 @@
 \usepackage{fontawesome5}
 \usepackage{hyperref}
 \usepackage[normalem]{ulem}
-\usepackage{ecsquare}
+
+\IfFileExists{ecsquare.sty}{\usepackage{ecsquare}}{}
 
 \definecolor{dkgreen}{rgb}{0,.5,0}
 \definecolor{dkblue}{rgb}{0,0,.6}