diff --git a/quad8/fiesta/homework/preamble.tex b/quad8/fiesta/homework/preamble.tex
index 75a52d4..217547f 100644
--- a/quad8/fiesta/homework/preamble.tex
+++ b/quad8/fiesta/homework/preamble.tex
@@ -124,3 +124,22 @@
 % Tensor commands:
 \newcommand*{\TT}[1]{\bar{\bar{#1}}}
 \newcommand*{\dev}[0]{\text{dev}\,}
+
+% Corrections:
+\newif\ifshowcorrections
+
+\newcommand{\correction}[1]{%
+  \ifshowcorrections%
+    {\color{red} #1}%
+  \else%
+    #1%
+  \fi%
+}%
+
+\newcommand{\formulacorrection}[1]{%
+  \ifshowcorrections%
+    \textcolor{red}{#1}%
+  \else%
+    #1%
+  \fi%
+}%