diff --git a/EPPlus/ExcelNamedRangeCollection.cs b/EPPlus/ExcelNamedRangeCollection.cs
index 8ea6462..3f6a493 100644
--- a/EPPlus/ExcelNamedRangeCollection.cs
+++ b/EPPlus/ExcelNamedRangeCollection.cs
@@ -81,6 +81,22 @@
 
         private void AddName(string Name, ExcelNamedRange item)
         {
+            // Is 'Name' already present
+            if (_dic.ContainsKey(Name))
+            {
+                int index = _dic[Name];
+                if ((0 <= index) && (index < _list.Count))
+                {
+                    ExcelNamedRange listItem = _list[index];
+                    if ((listItem != null) && (listItem.FullAddress == item.FullAddress))
+                        return;
+
+                    throw new Exception(string.Format("Name '{0}' is defined in the worksheet more than once. First as '{1}' and second as '{2}'.", Name, listItem.FullAddress, item.FullAddress));
+                }
+
+                throw new Exception(string.Format("Name '{0}' is defined in the worksheet more than once.", Name));
+            }
+
             _dic.Add(Name, _list.Count);
             _list.Add(item);
         }
diff --git a/EPPlus/FormulaParsing/CalculateExtentions.cs b/EPPlus/FormulaParsing/CalculateExtentions.cs
index 6763f3b..1ec584a 100644
--- a/EPPlus/FormulaParsing/CalculateExtentions.cs
+++ b/EPPlus/FormulaParsing/CalculateExtentions.cs
@@ -153,6 +153,11 @@
                     }
                     Thread.Sleep(0);
                 }
+                catch (OfficeOpenXml.FormulaParsing.Excel.Functions.FunctionException functionex)
+                {
+                    // Excel function is not supported by EPPlus
+                    throw (functionex);
+                }
                 catch (FormatException fe)
                 {
                     throw (fe);
diff --git a/EPPlus/FormulaParsing/Excel/Functions/FunctionRepository.cs b/EPPlus/FormulaParsing/Excel/Functions/FunctionRepository.cs
index ca4a769..4b90546 100644
--- a/EPPlus/FormulaParsing/Excel/Functions/FunctionRepository.cs
+++ b/EPPlus/FormulaParsing/Excel/Functions/FunctionRepository.cs
@@ -33,6 +33,29 @@
 
 namespace OfficeOpenXml.FormulaParsing.Excel.Functions
 {
+    // Used to report the names of Excel functions that are not supported by EPPlus
+    public class FunctionException : SystemException
+    {
+        // Summary:
+        //     Initializes a new instance of the System.FunctionException class.
+        public FunctionException()
+            : base()
+        {
+        }
+        //
+        // Summary:
+        //     Initializes a new instance of the System.FunctionException class with a specified
+        //     error message.
+        //
+        // Parameters:
+        //   message:
+        //     The message that describes the error.
+        public FunctionException(string message)
+            : base(message)
+        {
+        }
+    }
+
     /// <summary>
     /// This class provides methods for accessing/modifying VBA Functions.
     /// </summary>
@@ -69,6 +92,9 @@
         {
             if(!_functions.ContainsKey(name.ToLower(CultureInfo.InvariantCulture)))
             {
+                // Report that Excel function is not supported by EPPlus
+                throw new FunctionException(string.Format("Excel function '{0}' is not supported in formulas.", name));
+
                 //throw new InvalidOperationException("Non supported function: " + name);
                 //throw new ExcelErrorValueException("Non supported function: " + name, ExcelErrorValue.Create(eErrorType.Name));
                 return null;
diff --git a/EPPlus/FormulaParsing/ExpressionGraph/CompileResult.cs b/EPPlus/FormulaParsing/ExpressionGraph/CompileResult.cs
index 8074af0..d1959c6 100644
--- a/EPPlus/FormulaParsing/ExpressionGraph/CompileResult.cs
+++ b/EPPlus/FormulaParsing/ExpressionGraph/CompileResult.cs
@@ -102,7 +102,14 @@
                 }
                 else if (IsNumericString)
                 {
-                    return double.Parse(Result.ToString(), NumberStyles.Float, CultureInfo.InvariantCulture);
+                    try
+                    {
+                        return double.Parse(Result.ToString(), NumberStyles.Float, CultureInfo.InvariantCulture);
+                    }
+                    catch (Exception ex)
+                    {
+                        return 0;
+                    }
                 }
                 else if (Result is ExcelDataProvider.IRangeInfo)
                 {
diff --git a/EPPlus/FormulaParsing/ExpressionGraph/DecimalExpression.cs b/EPPlus/FormulaParsing/ExpressionGraph/DecimalExpression.cs
index 1182d2d..6e3ba50 100644
--- a/EPPlus/FormulaParsing/ExpressionGraph/DecimalExpression.cs
+++ b/EPPlus/FormulaParsing/ExpressionGraph/DecimalExpression.cs
@@ -65,5 +65,11 @@
             result = _negate ? result * -1 : result;
             return new CompileResult(result, DataType.Decimal);
         }
+
+        public bool IsNegated
+        {
+            get { return _negate; }
+        }
+
     }
 }
diff --git a/EPPlus/FormulaParsing/ExpressionGraph/ExcelAddressExpression.cs b/EPPlus/FormulaParsing/ExpressionGraph/ExcelAddressExpression.cs
index c034117..186c726 100644
--- a/EPPlus/FormulaParsing/ExpressionGraph/ExcelAddressExpression.cs
+++ b/EPPlus/FormulaParsing/ExpressionGraph/ExcelAddressExpression.cs
@@ -118,5 +118,11 @@
             compileResult.IsHiddenCell = cell.IsHiddenRow;
             return compileResult;
         }
+
+        public bool IsNegated
+        {
+            get { return _negate; }
+        }
+
     }
 }
diff --git a/EPPlus/FormulaParsing/ExpressionGraph/Expression.cs b/EPPlus/FormulaParsing/ExpressionGraph/Expression.cs
index 61ab6b3..277b78a 100644
--- a/EPPlus/FormulaParsing/ExpressionGraph/Expression.cs
+++ b/EPPlus/FormulaParsing/ExpressionGraph/Expression.cs
@@ -39,7 +39,7 @@
 {
     public abstract class Expression
     {
-        protected string ExpressionString { get; private set; }
+        public string ExpressionString { get; private set; }
         private readonly List<Expression> _children = new List<Expression>();
         public IEnumerable<Expression> Children { get { return _children; } }
         public Expression Next { get; set; }
diff --git a/EPPlus/FormulaParsing/ExpressionGraph/GroupExpression.cs b/EPPlus/FormulaParsing/ExpressionGraph/GroupExpression.cs
index cad1339..e8dba20 100644
--- a/EPPlus/FormulaParsing/ExpressionGraph/GroupExpression.cs
+++ b/EPPlus/FormulaParsing/ExpressionGraph/GroupExpression.cs
@@ -67,5 +67,11 @@
         {
             get { return true; }
         }
+
+        public bool IsNegated
+        {
+            get { return _isNegated; }
+        }
+
     }
 }
diff --git a/EPPlus/FormulaParsing/ExpressionGraph/IntegerExpression.cs b/EPPlus/FormulaParsing/ExpressionGraph/IntegerExpression.cs
index 6178660..4e57168 100644
--- a/EPPlus/FormulaParsing/ExpressionGraph/IntegerExpression.cs
+++ b/EPPlus/FormulaParsing/ExpressionGraph/IntegerExpression.cs
@@ -65,5 +65,11 @@
             result = _negate ? result*-1 : result;
             return new CompileResult(result, DataType.Integer);
         }
+
+        public bool IsNegated
+        {
+            get { return _negate; }
+        }
+
     }
 }
diff --git a/EPPlus/FormulaParsing/FormulaParser.cs b/EPPlus/FormulaParsing/FormulaParser.cs
index 64dd6cc..e025114 100644
--- a/EPPlus/FormulaParsing/FormulaParser.cs
+++ b/EPPlus/FormulaParsing/FormulaParser.cs
@@ -218,6 +218,17 @@
             }
         }
 
+        // Praveen's Formula Parser
+        public ExpressionGraph.ExpressionGraph ParseToGraph(string formula)
+        {
+            using (var scope = _parsingContext.Scopes.NewScope(RangeAddress.Empty))
+            {
+                var tokens = _lexer.Tokenize(formula);
+                var graph = _graphBuilder.Build(tokens);
+                return graph;
+            }
+        }
+
         public IFormulaParserLogger Logger
         {
             get { return _parsingContext.Configuration.Logger; }
diff --git a/EPPlus/FormulaParsing/FormulaParserManager.cs b/EPPlus/FormulaParsing/FormulaParserManager.cs
index 7137b99..aa9658b 100644
--- a/EPPlus/FormulaParsing/FormulaParserManager.cs
+++ b/EPPlus/FormulaParsing/FormulaParserManager.cs
@@ -97,6 +97,12 @@
             return _parser.Parse(formula);
         }
 
+        // Praveen's Parser Support
+        public ExpressionGraph.ExpressionGraph ParseToGraph(string formula)
+        {
+            return _parser.ParseToGraph(formula);
+        }
+
         /// <summary>
         /// Attaches a logger to the <see cref="FormulaParser"/>.
         /// </summary>
diff --git a/EPPlus/FormulaParsing/LexicalAnalysis/SourceCodeTokenizer.cs b/EPPlus/FormulaParsing/LexicalAnalysis/SourceCodeTokenizer.cs
index 60b9e9c..a0d5d47 100644
--- a/EPPlus/FormulaParsing/LexicalAnalysis/SourceCodeTokenizer.cs
+++ b/EPPlus/FormulaParsing/LexicalAnalysis/SourceCodeTokenizer.cs
@@ -71,6 +71,8 @@
             // MA 1401: Ignore leading plus in formula.
             input = input.TrimStart('+');
             var context = new TokenizerContext(input);
+
+            bool isSingleQuoteString = false;
             for (int i = 0; i<context.FormulaChars.Length;i++)
             {
                 var c = context.FormulaChars[i];
@@ -90,6 +92,12 @@
                             context.AppendToCurrentToken(c);
                             continue;
                         }
+                        // CHANGE 2
+                        if ((isSingleQuoteString && c != '\'') || (!isSingleQuoteString && c != '"'))
+                        {
+                            context.AppendToCurrentToken(c);
+                            continue;
+                        }
                     }
                     if (tokenSeparator.TokenType == TokenType.OpeningBracket)
                     {
@@ -119,9 +127,11 @@
                     }
                     if (tokenSeparator.TokenType == TokenType.String)
                     {
+                        // CHANGE3 :
+                        isSingleQuoteString = (c == '\'');
                         if (context.LastToken != null && context.LastToken.TokenType == TokenType.OpeningEnumerable)
                         {
-                            context.AppendToCurrentToken(c);
+                            // context.AppendToCurrentToken(c);  // Praveen's change of 10/28/2015
                             context.ToggleIsInString();
                             continue;
                         }
diff --git a/EPPlus/FormulaParsing/LexicalAnalysis/TokenSeparatorProvider.cs b/EPPlus/FormulaParsing/LexicalAnalysis/TokenSeparatorProvider.cs
index 61df09a..d11ccd6 100644
--- a/EPPlus/FormulaParsing/LexicalAnalysis/TokenSeparatorProvider.cs
+++ b/EPPlus/FormulaParsing/LexicalAnalysis/TokenSeparatorProvider.cs
@@ -59,7 +59,7 @@
             _tokens.Add(")", new Token(")", TokenType.ClosingParenthesis));
             _tokens.Add("{", new Token("{", TokenType.OpeningEnumerable));
             _tokens.Add("}", new Token("}", TokenType.ClosingEnumerable));
-            _tokens.Add("'", new Token("'", TokenType.String));
+            _tokens.Add("'", new Token("'", TokenType.String));  
             _tokens.Add("\"", new Token("\"", TokenType.String));
             _tokens.Add(",", new Token(",", TokenType.Comma));
             _tokens.Add(";", new Token(";", TokenType.SemiColon));
diff --git a/EPPlus/FormulaParsing/LexicalAnalysis/TokenizerContext.cs b/EPPlus/FormulaParsing/LexicalAnalysis/TokenizerContext.cs
index 5518a5c..6a28142 100644
--- a/EPPlus/FormulaParsing/LexicalAnalysis/TokenizerContext.cs
+++ b/EPPlus/FormulaParsing/LexicalAnalysis/TokenizerContext.cs
@@ -85,7 +85,7 @@
 
         public bool CurrentTokenHasValue
         {
-            get { return !string.IsNullOrEmpty(CurrentToken.Trim()); }
+            get { return !string.IsNullOrEmpty(this.IsInString ? CurrentToken : CurrentToken.Trim()); }
         }
 
         public void NewToken()