remove references from VPA

alib2data/src/automaton/PDA/VisiblyPushdownNPDA.cpp

@@ -188,15 +188,15 @@ bool VisiblyPushdownNPDA::removeTransition(const State& from, const alphabet::Sy
 	return localTransitions[key].erase(to);
 }
-const std::map<std::pair<State, alphabet::Symbol>, std::set<std::pair<State, alphabet::Symbol> > > VisiblyPushdownNPDA::getCallTransitions() const {
+const std::map<std::pair<State, alphabet::Symbol>, std::set<std::pair<State, alphabet::Symbol> > >& VisiblyPushdownNPDA::getCallTransitions() const {
 		return callTransitions;
 }
-const std::map<std::tuple<State, alphabet::Symbol, alphabet::Symbol>, std::set<State> > VisiblyPushdownNPDA::getReturnTransitions() const {
+const std::map<std::tuple<State, alphabet::Symbol, alphabet::Symbol>, std::set<State> >& VisiblyPushdownNPDA::getReturnTransitions() const {
 		return returnTransitions;
 }
-const std::map<std::pair<State, alphabet::Symbol>, std::set<State> > VisiblyPushdownNPDA::getLocalTransitions() const {
+const std::map<std::pair<State, alphabet::Symbol>, std::set<State> >& VisiblyPushdownNPDA::getLocalTransitions() const {
 		return localTransitions;
 }

alib2data/src/automaton/PDA/VisiblyPushdownNPDA.h

@@ -98,11 +98,11 @@ public:
 	 */
 	bool removeTransition(const State& current, const alphabet::Symbol& input, const State& next);
-	const std::map<std::pair<State, alphabet::Symbol>, std::set<std::pair<State, alphabet::Symbol> > > getCallTransitions() const;
-	const std::map<std::tuple<State, alphabet::Symbol, alphabet::Symbol>, std::set<State> > getReturnTransitions() const;
-	const std::map<std::pair<State, alphabet::Symbol>, std::set<State> > getLocalTransitions() const;
+	const std::map<std::pair<State, alphabet::Symbol>, std::set<std::pair<State, alphabet::Symbol> > >& getCallTransitions() const;
+	const std::map<std::tuple<State, alphabet::Symbol, alphabet::Symbol>, std::set<State> >& getReturnTransitions() const;
+	const std::map<std::pair<State, alphabet::Symbol>, std::set<State> >& getLocalTransitions() const;
 	virtual bool operator<(const alib::ObjectBase& other) const;
 	virtual bool operator==(const alib::ObjectBase& other) const;