diff --git a/srohtml.c b/srohtml.c
index b68839a..173a780 100644
--- a/srohtml.c
+++ b/srohtml.c
@@ -9,31 +9,61 @@
 #define CLS_MAX 16
 #define DATE_LEN 10
 #define FAVICON "data:image/gif;base64,R0lGODlhEAAQAKEAAAAAcP///wAAcAAAcCH5BAEKAAIALAAAAAAQABAAQAIwlBWZxxwAQWjtTQRvlZhTnGSfYT3eZ3WaE4mjGa1UasoH7c6tzYanfqmhJMKXglcAADs="
+#define INDEX_START 16
 #define LANG_LEN 2
 #define LINE_MAX 1000
 #define LINE_START 80
 #define NOTES_START 8
 #define NOTES_MAX_DIGITS 3
 
+typedef struct {
+	int indentation;
+	char *name;
+} closure;
+
+typedef struct {
+	int index;
+	int size;
+	closure *tags;
+} closures;
+
+typedef enum {
+	tag_content   = 0,
+	tag_attribute = 1
+} html_val_type;
+
+typedef struct {
+	size_t size;
+	char *str;
+} string;
+
+typedef struct {
+	char *desc;
+	char *id;
+	char heading;
+} index_title;
+
+typedef struct {
+	int index;
+	int size;
+	index_title *titles;
+} index;
+
 typedef struct {
 	char *desc;
 	char *href;
 } note;
 
 typedef struct {
-	size_t index;
-	size_t size;
+	int index;
 	note *notes;
+	int size;
 } references;
 
-typedef struct {
-	size_t len;
-	size_t size;
-	char *str;
-} string;
-
 /* function declarations */
-static size_t add_note(const char *href, const char *desc);
+static void add_closure(closures *dst, const char *tag, const int ind);
+static void add_h_to_index(const char heading, const char *id);
+static int add_note(const char *href, const char *desc);
 static void cmd(char *line);
 static void cmd_close(void);
 static void cmd_a(const char *line);
@@ -45,6 +75,7 @@ static void cmd_fi(const char *line);
 static void cmd_h(const char *line);
 static void cmd_hr(void);
 static void cmd_i(const char *line);
+static void cmd_in();
 static void cmd_la(const char *line);
 static void cmd_le(void);
 static void cmd_ls(void);
@@ -55,11 +86,16 @@ static void cmd_q(const char *line);
 static void cmd_st(const char *line);
 static void cmd_tm(const char *line);
 static void cmd_ur(const char *line);
+static void findent(const int ind, FILE *f);
 static void footer(void);
 static void footnotes(void);
+static int fputs_html(const char *str, FILE *f, const html_val_type t);
 static size_t fread_line(FILE *file, char **str, size_t *len);
-static void indent_str(char **str);
+static void free_closures(closures *dst);
+static void indent_str(char **str, const int ind);
+static void nav_index(FILE *f);
 static void page_head(void);
+static void pop_closure(closures *dst);
 static void print_help(void);
 static void print_usage(void);
 static void print_version(void);
@@ -67,27 +103,68 @@ static void *safe_malloc(const size_t size);
 static void *safe_realloc(void *ptr, const size_t size);
 static size_t stread_param(const char *src, char **str);
 static char *string_cat(string *dst, const char *src);
-static char *string_cat_html(string *dst, const char *src, const int is_attr_val);
+static char *string_cat_html(string *dst, const char *src, const html_val_type t);
 static void string_enlarge(string *old, const size_t size);
 static int string_putc(string *dst, const char c);
 
 /* variables */
-int imgs_presence = 0;
 char *author = NULL;
-char closure[CLS_MAX]; 
+string body;
 char *description = NULL;
+string head;
+size_t heading_position = 0;
+int imgs_presence = 0;
 int indentation = 2;
+size_t index_position = 0;
 char *language = NULL;
 int licence_container = 0;
-int space = 0;
-string head;
-string body;
+index page_index;
 char *pub_date = NULL;
 references sitography;
+int space = 0;
+char tag_closure[CLS_MAX];
 char *title = NULL; 
 
 /* function implementations */
-size_t
+void
+add_closure(closures *dst, const char *name, const int ind)
+{
+	closure *tag;
+
+	if (dst->index == dst->size) {
+		dst->size *= 2;
+		dst->tags = safe_realloc(dst->tags, sizeof(closure) * dst->size);
+	}
+
+	tag = dst->tags + dst->index;
+
+	tag->indentation = ind;
+	tag->name = safe_malloc(sizeof(char) * (strlen(name) + 1));
+	strcpy(tag->name, name);
+	dst->index++;
+}
+
+void
+add_h_to_index(const char heading, const char *id)
+{
+	index_title *new;
+
+	if (page_index.index == page_index.size) {
+		page_index.size *= 2;
+		page_index.titles = safe_realloc(page_index.titles, sizeof(index_title) * page_index.size);
+	}
+
+	new = page_index.titles + page_index.index;
+
+	new->desc = NULL;
+	new->heading = heading;
+	new->id = safe_malloc(sizeof(char) * (strlen(id) + 1));
+	strcpy(new->id, id);
+
+	heading_position = strlen(body.str);
+}
+
+int
 add_note(const char *href, const char *desc)
 {
 	note *new;
@@ -147,6 +224,8 @@ cmd(char *line)
 		cmd_hr();
 	else if (!strncmp(line, "I", cmdlen))
 		cmd_i(line);
+	else if (!strncmp(line, "IN", cmdlen))
+		cmd_in();
 	else if (!strncmp(line, "LA", cmdlen))
 		cmd_la(line);
 	else if (!strncmp(line, "LE", cmdlen))
@@ -199,11 +278,11 @@ cmd_a(const char *line)
 	string_cat(&body, "\"");
 	if (strcmp(title, "")) {
 		string_cat(&body, " title=\"");
-		string_cat_html(&body, title, 1);
+		string_cat_html(&body, title, tag_attribute);
 		string_cat(&body, "\"");
 	}
 	string_cat(&body, ">");
-	string_cat_html(&body, in, 1);
+	string_cat_html(&body, in, tag_attribute);
 	string_cat(&body, "</a>");
 	
 	free(href);
@@ -237,9 +316,28 @@ cmd_br(void)
 void
 cmd_close(void)
 {
-	string_cat(&body, closure);
+	index_title *title;
+
+	title = NULL;
+
+	if ((!strcmp(tag_closure, "</h3>") ||
+	     !strcmp(tag_closure, "</h4>") ||
+	     !strcmp(tag_closure, "</h5>") ||
+	     !strcmp(tag_closure, "</h6>")) &&
+	     index_position && heading_position) {
+
+		title = page_index.titles + page_index.index;
+
+		title->desc = safe_malloc(sizeof(char) * (strlen(body.str + heading_position) + 1));
+		strcpy(title->desc, body.str + heading_position);
+		page_index.index++;
+		heading_position = 0;
+	}
+
+	string_cat(&body, tag_closure);
 	string_cat(&body, "\n");
-	strcpy(closure, "");
+
+	strcpy(tag_closure, "");
 	space = 0;
 }
 
@@ -260,12 +358,12 @@ cmd_dt(const char *line)
 	if (space)
 		string_cat(&body, " ");
 	string_cat(&body, "<time datetime=\"");
-	string_cat_html(&body, datetime, 1);
+	string_cat_html(&body, datetime, tag_attribute);
 	string_cat(&body, "\">");
 	if (!strcmp(in, ""))
-		string_cat_html(&body, datetime, 0);
+		string_cat_html(&body, datetime, tag_content);
 	else
-		string_cat_html(&body, in, 0);
+		string_cat_html(&body, in, tag_content);
 	string_cat(&body, "</time>");
 
 	free(datetime);
@@ -301,7 +399,7 @@ cmd_fi(const char *line)
 	/* move past argument, once found it */
 	line += stread_param(line, &src);
 
-	indent_str(&ind);
+	indent_str(&ind, indentation);
 
 	string_cat(&body, ind);
 	string_cat(&body, "<figure><img src=\"");
@@ -315,18 +413,28 @@ cmd_fi(const char *line)
 void
 cmd_h(const char *line)
 {
+	const char *id;
+
+	id = NULL;
+
 	string_cat(&body, "\t\t<h");
 	string_putc(&body, line[1]);
-	if (line[2] == ' ' && line[3] != '\0') {
+	if (strlen(line) > 4 && line[2] == ' ' && line[3] != '\0') {
+		id = line + 3;
+
 		string_cat(&body, " id=\"");
-		string_cat_html(&body, line + 3, 1);
+		string_cat_html(&body, id, tag_attribute);
 		string_cat(&body, "\"");
 	}
 	string_cat(&body, ">");
-	strcpy(closure, "</h");
-	closure[3] = line[1];
-	closure[4] = '>';
-	closure[5] = '\0';
+
+	strcpy(tag_closure, "</h");
+	tag_closure[3] = line[1];
+	tag_closure[4] = '>';
+	tag_closure[5] = '\0';
+
+	if (id != NULL && index_position != 0)
+		add_h_to_index(line[1], id);
 }
 
 void
@@ -349,6 +457,14 @@ cmd_i(const char *line)
 	string_cat(&body, "<i>");
 	string_cat(&body, line);
 	string_cat(&body, "</i>");
+
+	space = 1;
+}
+
+void
+cmd_in(void)
+{
+	index_position = strlen(body.str);
 }
 
 void
@@ -379,7 +495,7 @@ cmd_le(void)
 	ind = NULL;
 
 	indentation--;
-	indent_str(&ind);
+	indent_str(&ind, indentation);
 	string_cat(&body, ind);
 	string_cat(&body, "</div>\n");
 
@@ -394,14 +510,14 @@ cmd_ls(void)
 	ind = NULL;
 	licence_container = 1;
 
-	indent_str(&ind);
+	indent_str(&ind, indentation);
 	string_cat(&body, ind);
 	string_cat(&body, "<div class=\"contenitore-licenza\">\n");
 	indentation++;
 
 	free(ind);
 	ind = NULL;
-	indent_str(&ind);
+	indent_str(&ind, indentation);
 	string_cat(&body, ind);
 	string_cat(&body, "<hr>\n");
 	
@@ -435,7 +551,7 @@ cmd_no(const char *line)
 	string_cat(&body, "\"");
 	if (strcmp(title, "")) {
 		string_cat(&body, " title=\"");
-		string_cat_html(&body, title, 1);
+		string_cat_html(&body, title, tag_attribute);
 		string_cat(&body, "\"");
 	}
 	string_cat(&body, ">[");
@@ -454,11 +570,11 @@ cmd_p(void)
 
 	ind = NULL;
 
-	indent_str(&ind);
+	indent_str(&ind, indentation);
 
 	string_cat(&body, ind);
 	string_cat(&body, "<p>");
-	strcpy(closure, "</p>");
+	strcpy(tag_closure, "</p>");
 
 	free(ind);
 }
@@ -500,12 +616,12 @@ cmd_q(const char *line)
 	string_cat(&body, "<q");
 	if (strcmp(cite, "")) {
 		string_cat(&body, " cite=\"");
-		string_cat_html(&body, cite, 1);
+		string_cat_html(&body, cite, tag_attribute);
 		string_cat(&body, "\"");
 	}
 	string_cat(&body, ">");
 	space = 0;
-	strcpy(closure, "</q></p>");
+	strcpy(tag_closure, "</q></p>");
 
 	free(cite);
 
@@ -514,13 +630,17 @@ cmd_q(const char *line)
 void
 cmd_st(const char *line)
 {
+	size_t len;
+
+	len = strlen(body.str);
+
 	/* move past "ST" */
 	line += 2;
 	/* move past space, if present */
 	if (line[0] == ' ')
 		line++;
 
-	if (space && body.str[body.len - 1] != '\'')
+	if (space && len > 0 && body.str[len - 1] != '\'')
 		string_cat(&body, " ");
 	string_cat(&body, "<strong>");
 	string_cat(&body, line);
@@ -548,7 +668,7 @@ cmd_tm(const char *line)
 		string_cat(&body, hours);
 	}
 	string_cat(&body, "\">");
-	string_cat_html(&body, in, 0);
+	string_cat_html(&body, in, tag_content);
 	string_cat(&body, "</time>");
 
 	free(date);
@@ -568,12 +688,24 @@ cmd_ur(const char *line)
 	if (space)
 		string_cat(&body, " ");
 	string_cat(&body, "&lt;<a class=\"url\" href=\"");
-	string_cat_html(&body, line, 1);
+	string_cat_html(&body, line, tag_attribute);
 	string_cat(&body, "\">");
-	string_cat_html(&body, line, 0);
+	string_cat_html(&body, line, tag_content);
 	string_cat(&body, "</a>&gt;");
 }
 
+void
+findent(const int ind, FILE *f)
+{
+	char *str;
+
+	str = NULL;
+
+	indent_str(&str, ind);
+	fputs(str, f);
+	free(str);
+}
+
 void
 footer(void)
 {
@@ -620,10 +752,10 @@ footer(void)
 	string_cat(&body, "\">");
 
 	strftime(str, max, "%x", now);
-	string_cat_html(&body, str, 0);
+	string_cat_html(&body, str, tag_content);
 
 	strftime(str, max, " %R", now);
-	string_cat_html(&body, str, 0);
+	string_cat_html(&body, str, tag_content);
 	string_cat(&body, "</time></p>\n");
 	
 	string_cat(&body, "\t\t</footer>\n");
@@ -633,7 +765,8 @@ void
 footnotes(void)
 {
 	note *cur;
-	size_t i, dig_num, x;
+	int i;
+	size_t dig_num, x;
 	char id[NOTES_MAX_DIGITS + 1];
 	char pad[6 * (NOTES_MAX_DIGITS - 1) + 1];
 
@@ -663,13 +796,13 @@ footnotes(void)
 		string_cat(&body, id);
 		string_cat(&body, "</a></span> ");
 		if (strcmp(cur->desc, "")) {
-			string_cat_html(&body, cur->desc, 0);
+			string_cat_html(&body, cur->desc, tag_content);
 			string_cat(&body, " ");
 		}
 		string_cat(&body, "&lt;<a class=\"url\" href=\"");
 		string_cat(&body, cur->href);
 		string_cat(&body, "\">");
-		string_cat_html(&body, cur->href, 0);
+		string_cat_html(&body, cur->href, tag_content);
 		string_cat(&body, "</a>&gt;</p>\n");
 		free(cur->desc);
 		free(cur->href);
@@ -679,6 +812,33 @@ footnotes(void)
 	string_cat(&body, "\t\t</div>\n");
 }
 
+int
+fputs_html(const char *str, FILE *f, const html_val_type t)
+{
+	size_t i, len;
+	int res;
+
+	len = strlen(str);
+	res = 0;
+
+	for (i = 0; i < len; i++) {
+		if (res == EOF)
+			return EOF;
+		if (t == tag_attribute && str[i] == '"')
+			res = fputs("&quot;", f);
+		else if (str[i] == '&')
+			res = fputs("&amp;", f);
+		else if (str[i] == '<')
+			res = fputs("&lt;", f);
+		else if (str[i] == '>')
+			res = fputs("&gt;", f);
+		else
+			res = fputc(str[i], f);
+	}
+
+	return 1;
+}
+
 size_t
 fread_line(FILE *file, char **str, size_t *len)
 {
@@ -707,14 +867,23 @@ fread_line(FILE *file, char **str, size_t *len)
 }
 
 void
-indent_str(char **str)
+free_closures(closures *dst)
 {
 	int i;
 
-	*str = safe_malloc(sizeof(char) * (indentation + 1));
-	for (i = 0; i < indentation; i++)
+	for (i = 0; i < dst->index; i++)
+		free(dst->tags[i].name);
+}
+
+void
+indent_str(char **str, const int ind)
+{
+	int i;
+
+	*str = safe_malloc(sizeof(char) * (ind + 1));
+	for (i = 0; i < ind; i++)
 		(*str)[i] = '\t';
-	(*str)[indentation] = '\0';
+	(*str)[ind] = '\0';
 }
 
 int
@@ -748,21 +917,23 @@ main (int argc, char *argv[])
 	}
 
 	head.size = BODY_START_SIZE / 4;
-	head.str = safe_malloc(head.size);
+	head.str = safe_malloc(sizeof(char) * head.size);
 	strcpy(head.str, "");
-	head.len = 0;
 
 	body.size = BODY_START_SIZE;
-	body.str = safe_malloc(body.size);
+	body.str = safe_malloc(sizeof(char) * body.size);
 	strcpy(body.str, "");
-	body.len = 0;
 
-	string_cat(&body, "\t<body>\n");
+	page_index.index = 0;
+	page_index.size = INDEX_START;
+	page_index.titles = safe_malloc(sizeof(index_title) * page_index.size);
 
 	sitography.index = 0;
 	sitography.size = NOTES_START;
 	sitography.notes = malloc(sizeof(note) * sitography.size);
 
+	string_cat(&body, "\t<body>\n");
+
 	len = 0;
 	line = NULL;
 	while (fread_line(in, &line, &len) != EOF) {
@@ -782,7 +953,7 @@ main (int argc, char *argv[])
 				line[0] != ';' &&
 				line[0] != '?')
 				string_cat(&body, " ");
-			string_cat_html(&body, line, 0);
+			string_cat_html(&body, line, tag_content);
 			space = 1;
 		}
 		free(line);
@@ -793,7 +964,7 @@ main (int argc, char *argv[])
 	if (in != stdin)
 		fclose(in);
 
-	if (strcmp(closure, ""))
+	if (strcmp(tag_closure, ""))
 		cmd_close();
 
 	page_head();
@@ -812,12 +983,104 @@ main (int argc, char *argv[])
 	}
 
 	fputs(head.str, out);
-	fputs(body.str, out);
+
+	{
+		char c;
+		c = body.str[index_position];
+		body.str[index_position] = '\0';
+		fputs(body.str, out);
+		if (index_position)
+			nav_index(out);
+		body.str[index_position] = c;
+		fputs(body.str + index_position, out);
+	}
+
 	fclose(out);
 
 	return 0;
 }
 
+void
+nav_index(FILE *f)
+{
+	int i, n;
+	int ind;
+	closure *tag;
+	closures nav_cls;
+	index_title *next_title, *title;
+
+	ind = 2;
+	nav_cls.index = 0;
+	nav_cls.size = 4;
+	nav_cls.tags = safe_malloc(sizeof(closure) * nav_cls.size);
+	tag = NULL;
+
+	findent(ind++, f);
+	fputs("<nav>\n", f);
+	findent(ind, f);
+	fputs("<hr>\n", f);
+	findent(ind, f);
+	fputs("<h3 id=\"indice\">Indice</h3>\n", f);
+	for (i = 0; i < page_index.index; i++) {
+		title = page_index.titles + i;
+		next_title = i == page_index.index - 1 ? NULL : title + 1;
+
+		if (i == 0) {
+			findent(ind, f);
+			fputs("<ul>\n", f);
+			add_closure(&nav_cls, "ul", ind);
+			ind++;
+		}
+
+		findent(ind, f);
+		fputs("<li><a href=\"#", f);
+		fputs_html(title->id, f, tag_attribute);
+		fprintf(f, "\">%s</a>", title->desc);
+		add_closure(&nav_cls, "li", ind);
+
+		if (i == page_index.index - 1) {
+			fputs("</li>\n", f);
+			ind--;
+			pop_closure(&nav_cls);
+			for (n = nav_cls.index - 1; n >= 0; n--) {
+				tag = nav_cls.tags + n;
+				findent(tag->indentation, f);
+				fprintf(f, "</%s>\n", tag->name);
+			}
+			findent(tag->indentation, f);
+			fputs("<hr>\n", f);
+			ind--;
+		} else if (next_title->heading < title->heading) {
+			fputs("</li>\n", f);
+			pop_closure(&nav_cls);
+			findent(--ind, f);
+			fputs("</ul>\n", f);
+			pop_closure(&nav_cls);
+			findent(--ind, f);
+			fputs("</li>\n", f);
+			pop_closure(&nav_cls);
+		} else if (next_title->heading > title->heading) {
+			fputs("\n", f);
+			findent(++ind, f);
+			fputs("<ul>\n", f);
+			add_closure(&nav_cls, "ul", ind);
+			ind++;
+		} else if ((title + 1)->heading == title->heading) {
+			fputs("</li>\n", f);
+			pop_closure(&nav_cls);
+		}
+
+		free(title->desc);
+		free(title->id);
+	}
+	findent(--tag->indentation, f);
+	fputs("</nav>\n", f);
+
+	free_closures(&nav_cls);
+	free(nav_cls.tags);
+	free(page_index.titles);
+}
+
 void
 page_head(void)
 {
@@ -826,7 +1089,7 @@ page_head(void)
 	string_cat(&head, "<html");
 	if (language != NULL) {
 		string_cat(&head, " lang=\"");
-		string_cat_html(&head, language, 1);
+		string_cat_html(&head, language, tag_attribute);
 		string_cat(&head, "\"");
 
 		free(language);
@@ -841,7 +1104,7 @@ page_head(void)
 
 	if (author != NULL) {
 		string_cat(&head, "\t\t<meta name=\"author\" content=\"");
-		string_cat_html(&head, author, 1);
+		string_cat_html(&head, author, tag_attribute);
 		string_cat(&head, "\">\n");
 
 		free(author);
@@ -849,7 +1112,7 @@ page_head(void)
 
 	if (description != NULL) {
 		string_cat(&head, "\t\t<meta name=\"description\" content=\"");
-		string_cat_html(&head, description, 1);
+		string_cat_html(&head, description, tag_attribute);
 		string_cat(&head, "\">\n");
 
 		free(description);
@@ -864,7 +1127,13 @@ page_head(void)
 "				width: 90%;\n" \
 "			}\n" \
 "\n" \
-"			p {\n" \
+"			p"
+	);
+	if (index_position)
+		string_cat(&head, ",\n\t\t\tli {");
+	else
+		string_cat(&head, " {");
+	string_cat(&head, "\n" \
 "				line-height: 1.5;\n" \
 "			}\n" \
 "\n" \
@@ -935,8 +1204,18 @@ page_head(void)
 "			@media print {\n" \
 "				body {\n" \
 "					max-width: 90%;\n" \
-"				}\n" \
-"\n" \
+"				}\n"
+	);
+
+	if (index_position) {
+		string_cat(&head, "\n" \
+"				nav {\n" \
+"					display: none;\n" \
+"				}\n"
+		);
+	}
+
+	string_cat(&head, "\n" \
 "				a.nav {\n" \
 "					color: inherit;\n" \
 "					text-decoration: none;\n" \
@@ -948,7 +1227,7 @@ page_head(void)
 
 	if (title != NULL) {
 		string_cat(&head, "\t\t<title>");
-		string_cat_html(&head, title, 0);
+		string_cat_html(&head, title, tag_content);
 		string_cat(&head, "</title>\n");
 
 		free(title);
@@ -994,6 +1273,19 @@ print_version(void)
 	exit(1);
 }
 
+void
+pop_closure(closures *dst)
+{
+	closure *tag;
+
+	if (dst->index <= 0)
+		return;
+
+	tag = dst->tags + (dst->index - 1);
+	free(tag->name);
+	dst->index--;
+}
+
 void *
 safe_malloc(const size_t size)
 {
@@ -1062,24 +1354,23 @@ string_cat(string *dst, const char *src)
 
 	len = strlen(src);
 
-	if (len >= (dst->size - dst->len))
+	if (len >= (dst->size - strlen(dst->str)))
 		string_enlarge(dst, (dst->size + len) * 2 + 1);
 
 	strcat(dst->str, src);
-	dst->len = dst->len + len;
 
 	return dst->str;
 }
 
 char *
-string_cat_html(string *dst, const char *src, const int is_attr_val)
+string_cat_html(string *dst, const char *src, const html_val_type t)
 {
 	size_t i, len;
 
 	len = strlen(src);
 
 	for (i = 0; i < len; i++) {
-		if (is_attr_val && src[i] == '"')
+		if (t == tag_attribute && src[i] == '"')
 			string_cat(dst, "&quot;");
 		else if (src[i] == '&')
 			string_cat(dst, "&amp;");
@@ -1104,12 +1395,15 @@ string_enlarge(string *old, const size_t size)
 int
 string_putc(string *dst, const char c)
 {
-	if ((dst->size - dst->len) <= 1)
+	size_t len;
+
+	len = strlen(dst->str);
+
+	if ((dst->size - len) <= 1)
 		string_enlarge(dst, (dst->size + 1) * 2 + 1);
 
-	dst->str[dst->len] = c;
-	dst->str[dst->len + 1] = '\0';
-	dst->len++;
+	dst->str[len] = c;
+	dst->str[len + 1] = '\0';
 
 	return (int) c;
 }