diff --git a/a3/binary_search_tree.c b/a3/binary_search_tree.c
index 89824ea..6075137 100644
--- a/a3/binary_search_tree.c
+++ b/a3/binary_search_tree.c
@@ -1,3 +1,21 @@
+#ifndef BINARY_SEARCH_TREE_H
+#define BINARY_SEARCH_TREE_H
+#include <stddef.h>
+
+typedef struct node node_t;
+
+struct node {
+   node_t *right;
+   node_t *left;
+   int data;
+};
+
+node_t *build_tree(int *tree_data, size_t tree_data_len);
+void free_tree(node_t *tree);
+int *sorted_data(node_t *tree);
+
+#endif
+
 #include "binary_search_tree.h"
 #include <stdlib.h>