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diff --git a/Chapters/Normalization.tex b/Chapters/Normalization.tex
index 714ce88..03f3792 100644
--- a/Chapters/Normalization.tex
+++ b/Chapters/Normalization.tex
@@ -641,8 +641,6 @@
       In the following sections, we will be using a number of functions and
       notations, which we will define here.
 
-      \todo{Define substitution (notation)}
-
       \subsubsection{Concepts}
         A \emph{global variable} is any variable (binder) that is bound at the
         top level of a program, or an external module. A \emph{local variable} is any
@@ -799,8 +797,33 @@
        optimizations, but they are required to get our program into intended
        normal form.
 
+        \placeintermezzo{}{
+          \startframedtext[width=8cm,background=box,frame=no]
+          \startalignment[center]
+            {\tfa Substitution notation}
+          \stopalignment
+          \blank[medium]
+
+          In some of the transformations in this chapter, we need to perform
+          substitution on an expression. Substitution means replacing every
+          occurence of some expression (usually a variable reference) with
+          another expression.
+
+          There have been a lot of different notations used in literature for
+          specifying substitution. The notation that will be used in this report
+          is the following:
+
+          \startlambda
+            E[A=>B]
+          \stoplambda
+
+          This means expression \lam{E} with all occurences of \lam{A} replaced
+          with \lam{B}.
+          \stopframedtext
+        }
+
+      \defref{beta-reduction}
       \subsubsection[sec:normalization:beta]{β-reduction}
-        \defref{beta-reduction}
         β-reduction is a well known transformation from lambda calculus, where it is
         the main reduction step. It reduces applications of lambda abstractions,
         removing both the lambda abstraction and the application.
@@ -1084,7 +1107,7 @@
 
         \transexample{apppropcase}{Application propagation for a case expression}{from}{to}
 
-      \subsubsection{Let recursification}
+      \subsubsection[sec:normalization:letrecurse]{Let recursification}
         This transformation makes all non-recursive lets recursive. In the
         end, we want a single recursive let in our normalized program, so all
         non-recursive lets can be converted. This also makes other