+ void AddBody(Body &);
+ void AddPlanet(Planet &);
+ void AddSun(Sun &);
+
+ Body &Root() noexcept { return root; }
+ const Body &Root() const noexcept { return root; }
+
+ const std::set<Body *> &Bodies() const noexcept { return bodies; }
+ const std::set<Planet *> &Planets() const noexcept { return planets; }
+ const std::set<Sun *> &Suns() const noexcept { return suns; }
+
+ double Time() const noexcept { return time; }