diff --git a/git-tutorial.css b/git-tutorial.css
index f7cee2e..d486b19 100644
--- a/git-tutorial.css
+++ b/git-tutorial.css
@@ -12,14 +12,14 @@ article#git-tutorial { max-width: 63rem; position: absolute; right:18.4em; top:0
 
 @media (max-width: 72em) {
     #git-tutorial td.cell-contents { width: 34em; }
-    #git-tutorial article { right: 7em; }
+    article#git-tutorial { right: 7em; }
     #git-tutorial #toc { right: -11em; }
     #git-tutorial #toc:hover { border-left: 5px solid gray; }
 }
 
 @media (max-width: 63em) {
     #git-tutorial td.cell-contents { width: 30em; }
-    #git-tutorial article { right:6em; }
+    article#git-tutorial { right:6em; }
     #git-tutorial #toc { right: -12em; }
     #git-tutorial #toc:hover { border-left: 5px solid gray; }
 }
@@ -27,7 +27,7 @@ article#git-tutorial { max-width: 63rem; position: absolute; right:18.4em; top:0
 #git-tutorial textarea { display:block; height: 18rem; }
 #git-tutorial .CodeMirror { height: max-content; }
 #git-tutorial input { display: inline-block; margin-right: 1em; font-size: 1.2rem; }
-#git-tutorial table, #git-tutorial td { border:thin solid black; border-collapse: collapse; }
+#git-tutorial table, #git-tutorial td, #git-tutorial th { border:thin solid black; border-collapse: collapse; }
 #git-tutorial .specialchar { color: red; word-wrap: normal; }
 #git-tutorial .hex-prefix { color: lightgrey; }
 #git-tutorial .hex { color: brown; }
@@ -43,7 +43,7 @@ article#git-tutorial { max-width: 63rem; position: absolute; right:18.4em; top:0
 #git-tutorial .error { color: orangered; }
 #git-tutorial .newline:after { content: ''; display:inline-block; width:100%; height:0; }
 #git-tutorial code { word-wrap: break-word; }
-#git-tutorial article .onlytoc { display: none; }
+article#git-tutorial .onlytoc { display: none; }
 /* #toc .onlytoc { } */
 #git-tutorial #toc .tocsmall { font-size: smaller; }
 #git-tutorial #toc .notoc { display: none; }
diff --git a/git-tutorial.js b/git-tutorial.js
index 5a0ad6e..dd53f28 100644
--- a/git-tutorial.js
+++ b/git-tutorial.js
@@ -361,7 +361,7 @@ function ___filesystem_to_string(fs) {
     + '<textarea id="elem-'+id+'" disabled="disabled" style="display:none">'
     + ___specialchars(___filesystem_to_printf(fs) || 'echo "Empty filesystem."')
     + '</textarea>'
-    + "<table>" + entries.join('') + "</table></div>";
+    + "<table><thead><tr><th>Path</th><th>Contents</th></tr></thead><tbody>" + entries.join('') + "</tbody></table></div>";
 }
 function ___textarea_value(elem) {
   if (elem.getValue) {
diff --git a/index.html b/index.html
index d9066d1..183158e 100644
--- a/index.html
+++ b/index.html
@@ -65,7 +65,7 @@ function read(filename) {
 }
 
 function write(filename, data) {
-  return filesystem[filename] = ""+data;
+  filesystem[filename] = String(data);
 }
 
 function exists(filename) {
@@ -73,11 +73,11 @@ function exists(filename) {
 }
 
 function mkdir(dirname) {
-  return filesystem[dirname] = null;
+  filesystem[dirname] = null;
 }
 
-function cd(d) {
-  current_directory = d;
+function cd(dirname) {
+  current_directory = dirname;
 }
 </textarea>
 </section>
@@ -105,8 +105,8 @@ function listdir(dirname) {
 <p>Our imaginary user will create a <code>proj</code> directory,
 and start filling in some files.</p>
 <textarea id="in3">
-cd('proj');
 mkdir('proj');
+cd('proj');
 write('proj/README', 'This is my Scheme project.\n');
 mkdir('proj/src');
 write('proj/src/main.scm', '(map (lambda (x) (+ x 1)) (list 1 2 3))\n');
@@ -118,7 +118,7 @@ write('proj/src/main.scm', '(map (lambda (x) (+ x 1)) (list 1 2 3))\n');
 <p>The first thing to do is to initialize the GIT directory.
 For now, only the <code>.git</code> folder is needed, The rest
 of the function implementing <code>git init</code> will be
-implemented later.</p>
+written later.</p>
 <textarea id="in4">
 function join_paths(a, b) {
   return (a == "") ? b : (a + "/" + b);
@@ -133,12 +133,11 @@ git_init_mkdir();
 </section>
 
 <section id="git-hash-object">
-<h1><code>git hash-object</code><span class="notoc" (storing a copy of a file in <code>.git</code>)</span></h1>
+<h1><code>git hash-object</code><span class="notoc"> (storing a copy of a file in <code>.git</code>)</span></h1>
 <p>The most basic element of a GIT repository is an object. It is a
 copy of a file that is stored in GIT&apos;s database. That copy is
 stored under a unique name. The unique name is obtained by hashing the
-contents of the file. <!-- or have a hash oracle that always returns a
-new number. --></p>
+contents of the file.</p>
 <textarea id="in5">
 function hash_object(must_write, type, is_data, path_or_data) {
   var data = is_data ? path_or_data : read(current_directory + "/" + path_or_data);
@@ -368,6 +367,60 @@ initial_commit = store_commit(
 </section>
 </section>
 
+<section id="resolving-references">
+<h1>resolving references</h1>
+<textarea>
+function trim_newline(s) {
+  if (s.endsWith('\n')) { return s.substr(0, s.length-1); } else { return s; }
+}
+</textarea>
+
+<section id="git-symbolic-ref">
+<h1><code>git symbolic-ref</code></h1>
+<textarea>
+function git_symbolic_ref(ref) {
+  var ref_file = join_paths(current_directory, '.git/' + ref);
+  if (exists(ref_file) && read(ref_file).startsWith('ref: ')) {
+    return trim_newline(read(ref_file)).substr('ref: '.length);
+  } else {
+    return false;
+  }
+}
+</textarea>
+</section>
+  
+<section id="git-rev-parse">
+<h1><code>git rev-parse</code></h1>  
+<textarea>
+function git_rev_parse(ref) {
+  var symbolic_ref_target = git_symbolic_ref(ref);
+  if (symbolic_ref_target) {
+    // symbolic ref like "ref: refs/heads/main"
+    return git_rev_parse(symbolic_ref_target);
+  } else if (/[0-9a-f]{40}/.test(ref)) {
+    // hash like "0123456789abcdef0123456789abcdef01234567"
+    return ref;
+  } else if (ref == 'HEAD') {
+    // user-friendly reference like "HEAD"
+    return git_rev_parse(trim_newline(read(join_paths(current_directory, '.git/' + ref))));
+  } else if (ref.startsWith('refs/') && exists(join_paths(current_directory, '.git/' + ref))) {
+    // user-friendly reference like "refs/heads/main"
+    return git_rev_parse(trim_newline(read(join_paths(current_directory, '.git/' + ref))));
+  } else if (exists(join_paths(current_directory, '.git/refs/heads/' + ref))) {
+    // user-friendly reference like "main" (a branch)
+    return git_rev_parse(trim_newline(read(join_paths(current_directory, '.git/refs/heads/' + ref))));
+  } else if (exists(join_paths(current_directory, '.git/refs/tags/' + ref))) {
+    // user-friendly reference like "v1.0" (a branch)
+    return git_rev_parse(trim_newline(read(join_paths(current_directory, '.git/refs/tags/' + ref))));
+  } else {
+    // unknown ref
+    return false;
+  }
+}
+</textarea>
+</section>
+</section>
+
 <section id="git-branch">
 <h1><code>git branch</code></h1>
 <p>A branch is a pointer to a commit, stored in a file in <code>.git/refs/heads/name_of_the_branch</code>.
@@ -456,48 +509,6 @@ function advance_head(new_commit_hash) {
 }
 </textarea>
 <textarea>
-function git_rev_parse(ref) {
-  var symbolic_ref_target = git_symbolic_ref(ref);
-  if (symbolic_ref_target) {
-    // symbolic ref like "ref: refs/heads/main"
-    return git_rev_parse(symbolic_ref_target);
-  } else if (/[0-9a-f]{40}/.test(ref)) {
-    // hash like "0123456789abcdef0123456789abcdef01234567"
-    return ref;
-  } else if (ref == 'HEAD') {
-    // user-friendly reference like "HEAD"
-    return git_rev_parse(trim_newline(read(join_paths(current_directory, '.git/' + ref))));
-  } else if (ref.startsWith('refs/') && exists(join_paths(current_directory, '.git/' + ref))) {
-    // user-friendly reference like "refs/heads/main"
-    return git_rev_parse(trim_newline(read(join_paths(current_directory, '.git/' + ref))));
-  } else if (exists(join_paths(current_directory, '.git/refs/heads/' + ref))) {
-    // user-friendly reference like "main" (a branch)
-    return git_rev_parse(trim_newline(read(join_paths(current_directory, '.git/refs/heads/' + ref))));
-  } else if (exists(join_paths(current_directory, '.git/refs/tags/' + ref))) {
-    // user-friendly reference like "v1.0" (a branch)
-    return git_rev_parse(trim_newline(read(join_paths(current_directory, '.git/refs/tags/' + ref))));
-  } else {
-    // unknown ref
-    return false;
-  }
-}
-</textarea>
-<textarea>
-function git_symbolic_ref(ref) {
-  var ref_file = join_paths(current_directory, '.git/' + ref);
-  if (exists(ref_file) && read(ref_file).startsWith('ref: ')) {
-    return trim_newline(read(ref_file)).substr('ref: '.length);
-  } else {
-    return false;
-  }
-}
-</textarea>
-<textarea>
-function trim_newline(s) {
-  if (s.endsWith('\n')) { return s.substr(0, s.length-1); } else { return s; }
-}
-</textarea>
-<textarea>
 write('proj/README', 'This is my Scheme project -- with updates!');
 var second_commit = git_commit(['README', 'src/main.scm'], 'Some updates');
 </textarea>
@@ -804,8 +815,8 @@ current_directory = '';
 </textarea>
 
 <textarea id="playground-play">
-cd('proj');
 mkdir('proj');
+cd('proj');
 write('proj/README', 'This is my implementation of GIT.\n');
 mkdir('proj/src');
 write('proj/src/main.scm', "(define filesystem '())\n...\n");