+inline TimeDelta operator*(T a, const TimeDelta &t) { return t*a; }
+
+void operator<<(LexicalConverter &, const TimeDelta &);
+
+
+// Constants to be used in creation of TimeDeltas
+extern const TimeDelta zero;
+extern const TimeDelta usec;
+extern const TimeDelta msec;
+extern const TimeDelta sec;
+extern const TimeDelta min;
+extern const TimeDelta hour;
+extern const TimeDelta day;
+extern const TimeDelta week;
+
+inline TimeDelta abs(const TimeDelta &t) { return t>=zero ? t : -t; }
+using std::abs;