diff --git a/CRAN-SUBMISSION b/CRAN-SUBMISSION
index fa2f140..dc838ba 100755
--- a/CRAN-SUBMISSION
+++ b/CRAN-SUBMISSION
@@ -1,3 +1,3 @@
-Version: 0.6.14
-Date: 2023-01-09 17:08:17 UTC
-SHA: 65b442c3e8df9be13917e8f8ce926ae8343929cc
+Version: 0.6.15
+Date: 2024-06-23 22:33:39 UTC
+SHA: 8b21a6bee9209be3ee5cd45d9129007755e7c4ce
diff --git a/src/appl-0.96/Core/SymbolSetIterator.h b/src/appl-0.96/Core/SymbolSetIterator.h
index c20a478..e3e6bd1 100755
--- a/src/appl-0.96/Core/SymbolSetIterator.h
+++ b/src/appl-0.96/Core/SymbolSetIterator.h
@@ -1,84 +1,72 @@
-#ifndef SymbolSetIterator_H
-#define SymbolSetIterator_H
-
-#include <iterator>
-
-#include "Const.h"
-using namespace std;
-//using namespace momdp;
-namespace momdp 
-{
-template <typename T> class SymbolSet;
-
-template <typename T>
-class SymbolSetIterator: public iterator<input_iterator_tag, T>
-{
-	SymbolSet<T> *parentSet;
-	int symbolID;
-
-
-public:
-	SymbolSetIterator(SymbolSet<T> *_parentSet, int _symbolID) 
-	{
-		parentSet = _parentSet;
-		symbolID = _symbolID;
-	}
-
-	SymbolSetIterator(const SymbolSetIterator& mit) 
-	{
-		this->parentSet = mit.parentSet;
-		this->symbolID = mit.symbolID;
-	}
-
-	SymbolSetIterator<T>& operator++() 
-	{
-		++symbolID;
-		return *this;
-	}
-
-	void operator++(int) 
-	{
-		symbolID++;
-	}
-
-	bool operator==(const SymbolSetIterator& rhs) 
-	{
-		if(parentSet == rhs.parentSet && symbolID == rhs.symbolID)
-		{
-			return true;
-		}
-		return false;
-	}
-
-	bool operator!=(const SymbolSetIterator& rhs) 
-	{
-		if(parentSet != rhs.parentSet || symbolID != rhs.symbolID)
-		{
-			return true;
-		}
-		return false;
-	}
-
-	int operator*() 
-	{
-		return symbolID;
-	}
-
-	T& value() 
-	{
-		return parentSet->getSymbol(symbolID);
-	}
-	int index() 
-	{
-		return symbolID;
-	}
-
-};
-
-}
-
-
-#endif
-
-
-
+// code edit assisted by ChatGPT 2024-06-24
+#ifndef SymbolSetIterator_H
+#define SymbolSetIterator_H
+
+#include <iterator>
+
+#include "Const.h"
+using namespace std;
+//using namespace momdp;
+
+namespace momdp
+{
+template <typename T> class SymbolSet;
+
+template <typename T>
+class SymbolSetIterator
+{
+  SymbolSet<T> *parentSet;
+  int symbolID;
+public:
+  using iterator_category = input_iterator_tag;
+  using value_type = T;
+  using difference_type = ptrdiff_t;
+  using pointer = T*;
+  using reference = T&;
+
+  SymbolSetIterator(SymbolSet<T> *_parentSet, int _symbolID)
+    : parentSet(_parentSet), symbolID(_symbolID) {}
+
+  SymbolSetIterator(const SymbolSetIterator& mit)
+    : parentSet(mit.parentSet), symbolID(mit.symbolID) {}
+
+  SymbolSetIterator<T>& operator++()
+  {
+    ++symbolID;
+    return *this;
+  }
+
+  SymbolSetIterator<T> operator++(int)
+  {
+    SymbolSetIterator<T> tmp(*this);
+    ++symbolID;
+    return tmp;
+  }
+
+  bool operator==(const SymbolSetIterator& rhs) const
+  {
+    return parentSet == rhs.parentSet && symbolID == rhs.symbolID;
+  }
+
+  bool operator!=(const SymbolSetIterator& rhs) const
+  {
+    return !(*this == rhs);
+  }
+
+  int operator*() const
+  {
+    return symbolID;
+  }
+
+  T& value() const
+  {
+    return parentSet->getSymbol(symbolID);
+  }
+
+  int index() const
+  {
+    return symbolID;
+  }
+};
+}
+#endif