diff --git a/libftasm/includes/btree.h b/libftasm/includes/btree.h
index 5839155c..4b3fd15d 100644
--- a/libftasm/includes/btree.h
+++ b/libftasm/includes/btree.h
@@ -36,6 +36,7 @@ typedef struct s_btree		t_btree;
 typedef struct s_printdata	t_printdata;
 
 t_btree	*btree_create_node(void const *item, size_t content_size);
+t_btree	*btree_map(t_btree *root, void *(*f)(void *))
 void	btree_insert_data(
 		t_btree **root,
 		void *item,
diff --git a/libftasm/includes/math.h b/libftasm/includes/math.h
index 26c1dcd6..6b372f7d 100644
--- a/libftasm/includes/math.h
+++ b/libftasm/includes/math.h
@@ -1,5 +1,4 @@
-/* ************************************************************************** */
-/*                                                                            */
+/* ************************************************************************** */ /*                                                                            */
 /*                                                        :::      ::::::::   */
 /*   math.h                                             :+:      :+:    :+:   */
 /*                                                    +:+ +:+         +:+     */
@@ -33,5 +32,6 @@ size_t	ft_lllen(long long n);
 size_t	ft_lllen_base(long long n, int base);
 
 int		ft_addrcmp(void *a, void *b);
+void	*id(void *data);
 
 #endif
diff --git a/libftasm/src/btree/btree_map.c b/libftasm/src/btree/btree_map.c
index bdf27e07..04d16491 100644
--- a/libftasm/src/btree/btree_map.c
+++ b/libftasm/src/btree/btree_map.c
@@ -1,13 +1,13 @@
 #include "btree.h"
 
-t_btree		*btree_map(t_btree *root, void *(*f)(void *item))
+t_btree		*btree_map(t_btree *root, void *(*f)(void *))
 {
 	t_btree		*new;
 
 	if (!root)
 		return (NULL);
 	new = btree_create_node(root->item, root->content_size);
-	new->item = (*f)(root->item);
+	new->item = (*f)(new->item);
 	new->left = btree_map(root->left, f);
 	new->right = btree_map(root->right, f);
 	return (new);
diff --git a/libftasm/src/math/id.c b/libftasm/src/math/id.c
new file mode 100644
index 00000000..938cb5d1
--- /dev/null
+++ b/libftasm/src/math/id.c
@@ -0,0 +1,6 @@
+#include "libft.h"
+
+void	*id(void *data)
+{
+	return (data);
+}