diff --git a/default.nix b/default.nix
index d5104bda063627c64020a77704e67c0d90634efd..83685bd5153e112e55cacc8d73f3b94c8f5f3ce1 100644
--- a/default.nix
+++ b/default.nix
@@ -1,4 +1,5 @@
 with import <nixpkgs> {};
+
 let texlive = pkgs.texlive.combine {
     inherit (pkgs.texlive)
     everypage
@@ -24,7 +25,9 @@ let texlive = pkgs.texlive.combine {
     comment
     dirtree ;
   };
+  inputs = [ texlive pkgs.dia rubber ninja ];
 in
+
 stdenv.mkDerivation rec {
   name="paper";
   src = ./.;
@@ -33,5 +36,10 @@ stdenv.mkDerivation rec {
     mkdir $out
     cp paper.pdf $out
     '';
-  buildInputs = [ texlive pkgs.dia rubber ninja ];
+  buildInputs = inputs;
+  shell = mkShell {
+    buildInputs = inputs;
+    shellHook = "ls | entr make";
+  };
+
 }
diff --git a/slides.pdf b/slides.pdf
index dbcb31669971af30459497a6c5ac2cfd0e7491df..ff575bc93791698a559f3897b7df5406f191307d 100644
Binary files a/slides.pdf and b/slides.pdf differ
diff --git a/slides.tex b/slides.tex
index 0e6a9b31f3a01dfa2c1fd54b72ed64ef6dc764c0..528fd1c7bdd319f13eb5e0baca819ca8190bac96 100644
--- a/slides.tex
+++ b/slides.tex
@@ -14,7 +14,7 @@
 \usepackage{array,booktabs}
 \usepackage{pgfpages}
 \usepackage{listings}
-%\setbeameroption{show notes on second screen=right}
+\setbeameroption{show notes on second screen=right}
 \lstset{language=Bash}
 
 \definecolor{identifiercolor}{rgb}{0,0,0}
@@ -314,7 +314,7 @@ The running environment should be explicit:
 
 \section{Nix Structure}
 
-\begin{frame}{Main Concept}
+\begin{frame}{Main Concepts}
 
   % Nix borrows its concept from Functional Languages. \\
     \begin{tcolorbox}[colframe=black,colback=gray!10,coltext=black]
@@ -323,26 +323,30 @@ The running environment should be explicit:
   \vspace{1em}
 
   Each software building action is described through functions.
-  \note{Function into the Functional paradigm point of view}
+  \note{Function from a functional paradigm point of view}
 
   \vspace{1em}
   Packages dependencies are also functions given as inputs.
 
+  \vspace{1em}
+  Such functions are called \textbf{Derivations}
+
 \end{frame}
 
 \begin{frame}[fragile]{Derivations}
- \note{https://nixos.org/nixos/nix-pills/our-first-derivation.html\\}
-     % Nix refers to \textbf{derivation} instead of package. \\
-  % A package is a defined by a \textbf{derivation}. \\
+  \note{https://nixos.org/nixos/nix-pills/our-first-derivation.html\\}
+      % Nix refers to \textbf{derivation} instead of package. \\
+   % A package is a defined by a \textbf{derivation}. \\
 
-  % It can be build with the command \textit{nix-build}.
+   % It can be build with the command \textit{nix-build}.
   \begin{tcolorbox}[colframe=black,colback=gray!10,coltext=black]
     A derivation is a Nix build action.
   \end{tcolorbox}
   \begin{onlyenv}<2>
 
   \vspace{1em}
-  It is an attribute set describing how to build a package.
+  It is a Nix attribute set describing how to build a package.
+  \note{A python dict, or java hashtable\\}
 
   \end{onlyenv}
   \pause
@@ -373,12 +377,29 @@ stdenv.mkDerivation {
 \begin{frame}[fragile]{Store}
 
 \begin{tcolorbox}[colframe=black,colback=gray!10,coltext=black]
-Nix uses a single directory to store every packages.
+  The command \textit{nix-build} builds a derivation.
+\end{tcolorbox}
+
+  \vspace{1em}
+
+The result of the build action is automatically placed into the nix store.
+
+  \begin{lstlisting}[basicstyle=\small]
+                  /nix/store/
+  \end{lstlisting}
+
+\end{frame}
+
+\begin{frame}[fragile]{Store}
+
+\begin{tcolorbox}[colframe=black,colback=gray!10,coltext=black]
+  Every packages (or derivations) are located into a common place: The store.
+% Nix uses a single directory to store every packages.
 \end{tcolorbox}
 
   \vspace{1em}
 
-  A packagesr is identified with a sha-256 hash of the source nix file and
+  A package is identified with a sha-256 hash of the nix source file and
   its "inputs".
 
   \begin{lstlisting}[basicstyle=\small]
@@ -396,25 +417,31 @@ Nix uses a single directory to store every packages.
 
 \end{frame}
 
-\begin{frame}[plain]{Nixpkgs}
+% \subsection{NixPkgs}
 
-\begin{tcolorbox}[colframe=black,colback=gray!10,coltext=black]
-  \center
-  NixPkgs is an open source git repository.
-\end{tcolorbox}
+\begin{frame}[fragile]{Nixpkgs}
 
-  \only<1>{
-    \vspace{1em}
-    It contains the derivations of all application (and libraries) \emph{officialy} available with Nix. \\
-  }
-  \only<1>{
-    \vspace{1em}
-    In short, \textbf{packages are declared as source code}.
-  }
+  How and where can we get derivations ?
+
+  \pause
+  \vspace{1em}
 
+  Derivations are source code:
+
+  \vspace{1em}
+  \begin{tcolorbox}[colframe=black,colback=gray!10,coltext=black]
+    \center
+    https://github.com/NixOS/nixpkgs \\
+    \textit{A.K.A} \textbf{NixPkgs}
+  \end{tcolorbox}
+
+  \vspace{1em}
+
+  NixPkgs contains the derivations of all application (and libraries) \emph{officialy} available with Nix.
 \end{frame}
 
-\begin{frame}[plain]{Channels}
+
+\begin{frame}[fragile]{Channels}
 
   \only<1>{
 
@@ -451,7 +478,7 @@ Nix uses a single directory to store every packages.
 % 
 % \end{frame}
 
-\begin{frame}[plain,noframenumbering]
+\begin{frame}[fragile,noframenumbering]
   \center Thanks. Question Time.
 \end{frame}