+void object_init (Object *object, double x, double y, double mass);
+void offset_spring_init (OffsetSpring *spring,
+ Object *a, Object *b, double dx, double dy);
+void spring_init (Spring *spring, Object *a, Object *b, double length);
+void stick_init (Stick *stick, Object *a, Object *b, double length);
+void string_init (String *string, Object *a, Object *b, double length);
+void spacer_init (Spacer *spacer, Object *a, Object *b, double length);
+void anchor_init (Anchor *anchor, Object *object, double x, double y);
+
+void polygon_init (Polygon *p, int enclosing, int num_points, ...);