+/* Concatenate arguments. _XBT_CONCAT2 adds a level of indirection over _XBT_CONCAT. */
+#define _XBT_CONCAT(a, b) a##b
+#define _XBT_CONCAT2(a, b) _XBT_CONCAT(a, b)
+#define _XBT_CONCAT3(a, b, c) _XBT_CONCAT2(_XBT_CONCAT2(a, b), c)
+#define _XBT_CONCAT4(a, b, c, d) _XBT_CONCAT2(_XBT_CONCAT3(a, b, c), d)