diff --git a/tools/Building.org b/tools/Building.org
index 6f1794a..32ccf3f 100644
--- a/tools/Building.org
+++ b/tools/Building.org
@@ -411,4 +411,132 @@ EOF
   #+end_src
 
 * Script to build the documentation
-* Script to build the documentation
+  :PROPERTIES:
+  :header-args:bash: :tangle build_doc.sh :noweb  yes :shebang #!/bin/bash :comments org
+  :END:
+
+  First define readonly global variables.
+  
+  #+begin_src bash :noweb yes
+readonly DOCS=${QMCKL_ROOT}/docs/
+readonly SRC=${QMCKL_ROOT}/src/
+readonly HTMLIZE=${DOCS}/htmlize.el
+readonly CONFIG_DOC=${QMCKL_ROOT}/tools/config_doc.el  
+readonly CONFIG_TANGLE=${QMCKL_ROOT}/tools/config_tangle.el  
+  #+end_src
+
+  Check that all the defined global variables correspond to files.
+
+  #+begin_src bash :noweb yes
+function check_preconditions()
+{
+    if [[ -z ${QMCKL_ROOT} ]]
+    then
+        print "QMCKL_ROOT is not defined"
+        exit 1
+    fi
+
+    for dir in ${DOCS} ${SRC}
+    do
+        if [[ ! -d ${dir} ]]
+        then
+            print "${dir} not found"
+            exit 2
+        fi
+    done
+    
+    for file in ${CONFIG_DOC} ${CONFIG_TANGLE}
+    do
+        if [[ ! -f ${file} ]]
+        then
+            print "${file} not found"
+            exit 3
+        fi
+    done
+}
+  #+end_src
+
+  ~install_htmlize~ installs the htmlize Emacs plugin if the
+  =htmlize.el= file is not present.
+
+  #+begin_src bash :noweb yes
+function install_htmlize()
+{
+    local url="https://github.com/hniksic/emacs-htmlize"
+    local repo="emacs-htmlize"
+    
+    [[ -f ${HTMLIZE} ]] || (
+        cd ${DOCS}
+        git clone ${url} \
+            && cp ${repo}/htmlize.el ${HTMLIZE} \
+            && rm -rf ${repo}
+        cd -
+    )
+
+    # Assert htmlize is installed
+    [[ -f ${HTMLIZE} ]] \
+        || exit 1
+}
+  #+end_src
+
+  Extract documentation from an org-mode file.
+
+  #+begin_src bash :noweb yes
+function extract_doc()
+{
+    local org=$1
+    local local_html=${SRC}/${org%.org}.html 
+    local html=${DOCS}/${org%.org}.html 
+
+    if [[ -f ${html} && ${org} -ot ${html} ]]
+    then
+        return
+    fi
+    emacs --batch                    \
+          --load ${HTMLIZE}          \
+          --load ${CONFIG_DOC}       \
+          ${org}                     \
+          --load ${CONFIG_TANGLE}    \
+          -f org-html-export-to-html 
+    mv ${local_html} ${DOCS}
+
+}
+  #+end_src
+
+  The main function of the script.
+  
+  #+begin_src bash :noweb yes
+function main() {
+    
+    [[ check_preconditions ]] \
+        || exit 1
+    
+    # Install htmlize if needed
+    [[ install_htmlize ]] \
+        || exit 2
+
+    # Create documentation
+    cd ${SRC} \
+        || exit 3
+
+    for i in *.org
+    do
+        echo
+        echo "=======  ${i} ======="
+        extract_doc ${i}
+    done
+
+    if [[ $? -eq 0 ]]
+    then
+        cd ${DOCS}
+        rm -f index.html
+        ln README.html index.html
+        exit 0
+    else
+        exit 3
+    fi
+}
+main
+  #+end_src
+
+
diff --git a/tools/build_doc.sh b/tools/build_doc.sh
index 11b06ac..6eede96 100755
--- a/tools/build_doc.sh
+++ b/tools/build_doc.sh
@@ -1,57 +1,132 @@
-#!/bin/bash 
+#!/bin/bash
+# Script to build the documentation
+#   :PROPERTIES:
+#   :header-args:bash: :tangle build_doc.sh :noweb  yes :shebang #!/bin/bash :comments org
+#   :END:
 
-if [[ -z $QMCKL_ROOT ]]
-then
-  print "QMCKL_ROOT is not defined"
-  exit 1
-fi
+#   First define readonly global variables.
+  
+
+readonly DOCS=${QMCKL_ROOT}/docs/
+readonly SRC=${QMCKL_ROOT}/src/
+readonly HTMLIZE=${DOCS}/htmlize.el
+readonly CONFIG_DOC=${QMCKL_ROOT}/tools/config_doc.el  
+readonly CONFIG_TANGLE=${QMCKL_ROOT}/tools/config_tangle.el
 
 
-# Install htmlize if needed
-[[ -f ${QMCKL_ROOT}/docs/htmlize.el ]] || (
-    cd ${QMCKL_ROOT}/docs/
-    git clone https://github.com/hniksic/emacs-htmlize 
-    cp emacs-htmlize/htmlize.el .
-    rm -rf emacs-htmlize
-    cd -
-)
 
-[[ -f ${QMCKL_ROOT}/docs/htmlize.el ]] || exit 1
+# Check that all the defined global variables correspond to files.
 
 
-# Create documentation
-cd ${QMCKL_ROOT}/src
+function check_preconditions()
+{
+    if [[ -z ${QMCKL_ROOT} ]]
+    then
+        print "QMCKL_ROOT is not defined"
+        exit 1
+    fi
+
+    for dir in ${DOCS} ${SRC}
+    do
+        if [[ ! -d ${dir} ]]
+        then
+            print "${dir} not found"
+            exit 2
+        fi
+    done
+    
+    for file in ${CONFIG_DOC} ${CONFIG_TANGLE}
+    do
+        if [[ ! -f ${file} ]]
+        then
+            print "${file} not found"
+            exit 3
+        fi
+    done
+}
+
+
+
+# ~install_htmlize~ installs the htmlize Emacs plugin if the
+# =htmlize.el= file is not present.
+
+
+function install_htmlize()
+{
+    local url="https://github.com/hniksic/emacs-htmlize"
+    local repo="emacs-htmlize"
+    
+    [[ -f ${HTMLIZE} ]] || (
+        cd ${DOCS}
+        git clone ${url} \
+            && cp ${repo}/htmlize.el ${HTMLIZE} \
+            && rm -rf ${repo}
+        cd -
+    )
+
+    # Assert htmlize is installed
+    [[ -f ${HTMLIZE} ]] \
+        || exit 1
+}
+
+
+
+# Extract documentation from an org-mode file.
+
 
 function extract_doc()
 {
-    HTML=${1%.org}.html 
-    if [[ -f ${QMCKL_ROOT}/docs/$HTML && $1 -ot ${QMCKL_ROOT}/docs/$HTML ]]
-    then return
+    local org=$1
+    local local_html=${SRC}/${org%.org}.html 
+    local html=${DOCS}/${org%.org}.html 
+
+    if [[ -f ${html} && ${org} -ot ${html} ]]
+    then
+        return
     fi
-    emacs --batch \
-          --load ${QMCKL_ROOT}/docs/htmlize.el \
-          --load ${QMCKL_ROOT}/tools/config_doc.el  \
-          $i \
-          --load ${QMCKL_ROOT}/tools/config_tangle.el  \
-          -f org-html-export-to-html || break
-    mv $HTML ${QMCKL_ROOT}/docs 
+    emacs --batch                    \
+          --load ${HTMLIZE}          \
+          --load ${CONFIG_DOC}       \
+          ${org}                     \
+          --load ${CONFIG_TANGLE}    \
+          -f org-html-export-to-html 
+    mv ${local_html} ${DOCS}
+
 }
 
-for i in *.org
-do
-echo
-echo "=======  $i ======="
-   extract_doc $i
-done
-
-if [[ $? -eq 0 ]]
-then
-  cd ${QMCKL_ROOT}/docs
-  rm -f index.html
-  ln README.html index.html
-  exit 0
-else
-  exit 2
-fi
 
 
+# The main function of the script.
+
+
+function main() {
+    
+    [[ check_preconditions ]] \
+        || exit 1
+    
+    # Install htmlize if needed
+    [[ install_htmlize ]] \
+        || exit 2
+
+    # Create documentation
+    cd ${SRC} \
+        || exit 3
+
+    for i in *.org
+    do
+        echo
+        echo "=======  ${i} ======="
+        extract_doc ${i}
+    done
+
+    if [[ $? -eq 0 ]]
+    then
+        cd ${DOCS}
+        rm -f index.html
+        ln README.html index.html
+        exit 0
+    else
+        exit 3
+    fi
+}
+main
diff --git a/tools/config_tangle.el b/tools/config_tangle.el
index 73b613d..6f1eed1 100755
--- a/tools/config_tangle.el
+++ b/tools/config_tangle.el
@@ -42,4 +42,5 @@
 (setq h_private  (concat name "_private.h"))
 (setq c_test  (concat pwd "test_" name ".c"))
 (setq f_test  (concat pwd "test_" name "_f.f90"))
+(org-babel-lob-ingest "../tools/lib.org")