+/**
+ * @addtogroup XBT_swag
+ * @brief a O(1) set based on linked lists
+ *
+ * <center><table><tr><td><b>Top</b> <td> [\ref index]::[\ref XBT_API]
+ * <tr><td><b>Prev</b> <td> [\ref XBT_fifo]
+ * <tr><td><b>Next</b> <td> [\ref XBT_heap]
+ * <tr><td><b>Down</b> <td> [\ref XBT_swag_type] </table></center>
+ *
+ * Warning, this module is done to be efficient and performs tons of
+ * cast and dirty things. So make sure you know what you are doing while using it.
+ * It is basically a fifo but with restrictions so that
+ * it can be used as a set. Any operation (add, remove, belongs) is O(1) and
+ * no call to malloc/free is done.
+ *
+ */