diff --git a/chap2.tex b/chap2.tex
index 55f3797..7d605b8 100644
--- a/chap2.tex
+++ b/chap2.tex
@@ -380,3 +380,5 @@ \subsection{Commands}
 \texttt{git status} - Show the status of tracked, changed, untracked files
 \subsection{Terminology}
 \textbf{Branch} - A way of working on the same set of code in parallel without modifications overlapping
+
+\textbf{Commit} - A group of objects and a tree in a Git repository
diff --git a/chap3.tex b/chap3.tex
index bb84b03..b51209b 100644
--- a/chap3.tex
+++ b/chap3.tex
@@ -247,9 +247,17 @@ \subsection{Commands}
 
 \texttt{git log -S<string> <path>} - Show all commits that either introduced or removed a particular string from the repository, but restrict the search to a specific path
 
+\texttt{git log HEAD~1..HEAD} - Show all commits between HEAD~1 and HEAD, essentially the last commit
+
+\texttt{git diff HEAD~1..HEAD} - Show the actual differences between HEAD~1 and HEAD
+
 \subsection{Terminology}
 \textbf{Branch} - A way of working on the same set of code in parallel without modifications overlapping
 
+\textbf{Diff} - Shows the actual differences between files
+
+\textbf{Hunk} - A section of a diff output
+
 %git log -p
 %DIFFs
 %Patching
diff --git a/chap4.tex b/chap4.tex
new file mode 100644
index 0000000..76f921a
--- /dev/null
+++ b/chap4.tex
@@ -0,0 +1,8 @@
+% chap4.tex - Week 4
+\cleardoublepage
+%\phantomsection
+\chapter{Week 4}
+\section{Day 1 - ``Finally we're getting somehere''}
+\subsection{Planting trees}
+%branches
+%merge
diff --git a/gitt.tex b/gitt.tex
index db1af74..243360d 100644
--- a/gitt.tex
+++ b/gitt.tex
@@ -75,6 +75,7 @@
 \input{chap1}
 \input{chap2}
 \input{chap3}
+\input{chap4}
 \input{ack}
 
 \end{document}