error: list<> does not contain a definition for ' '

Hi all,
I'm getting this error for my following program, can anyone explain the below error and how can i solve it?
thanks in advance.

error CS1061: 'System.Collections.Generic.List<AbstractSyntax.Declaration>' does not contain a definition for 'toStringIndented' and no extension method 'toStringIndented' accepting a first argument of type 'System.Collections.Generic.List<AbstractSyntax.Declaration>' could be found (are you missing a using directive or an assembly reference?)

in my abstractsyntax.cs:

public class CProgram
    {
        List<Declaration> decpart = new List<Declaration>();
        List<Statement> body = new List<Statement>();

        public CProgram(List<Declaration> d, List<Statement> b)
        {
            decpart = d;
            body = b;
        }

        public String toString()
        {
            return toStringIndented("");
        }
        public String toStringIndented(String indent)
        {
            return indent + "Program(\n"
              + decpart.toStringIndented(indent + "  ") + ",\n" <-- error
              + body.toStringIndented(indent + "  ") + "\n" <-- error
              + indent + ")";
        }
    }

public class Declaration
    {
        public List<Declaration> decl = null;

        public Declaration()
        {

        }

        public Declaration(List<Declaration> Declarations)
        {
            this.decl = Declarations;
        }

        public String toString()
        {
            return toStringIndented("");
        }

        public String toStringIndented(String indent)
        {
            StringBuilder sb = new StringBuilder();
            sb.Append(indent);
            sb.Append("Declarations(\n");
            int i = 0;
            foreach (Declaration s in decl)
            {
                sb.Append(this.toStringIndented(indent + "  "));
                i++;
                if (i == decl.Count)
                    sb.Append("\n");
                else
                    sb.Append(",\n");
            }
            sb.Append(indent);
            sb.Append(")");
            return sb.ToString();
        }
    }

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in my parser.cs:

public void program()
        {
            match(Token.TokenType.Int);
            match(Token.TokenType.Main);
            match(Token.TokenType.LeftParen);
            match(Token.TokenType.RightParen);
            match(Token.TokenType.LeftBrace);
            List<Declaration> decls = declarations();
            List<Statement> stmts = statements();
            match(Token.TokenType.RightBrace);

            if (error_flag == false)
                Console.WriteLine("No Syntax Error. Comgratulation!");

            CProgram p = new CProgram(decls,stmts);
        }

        private List<Declaration> declarations()
        {
            List<Declaration> ds = new List<Declaration>();
            List<Declaration> dsl = new List<Declaration>();
            while (current_token.getType() == Token.TokenType.Int ||
                current_token.getType() == Token.TokenType.Float ||
                current_token.getType() == Token.TokenType.Char ||
                current_token.getType() == Token.TokenType.Bool)
            {
                dsl = declaration();
                ds.AddRange(dsl);
            }
            return ds; 
        }

        private List<Declaration> declaration()
        {
            List<Declaration> result = new List<Declaration>();
            Type t = type();
            Variable v = new Variable(match(Token.TokenType.Identifier));

            if (current_token.getType() == Token.TokenType.LeftBracket)
            {
                match(Token.TokenType.LeftBracket);
                int i = Convert.ToInt32(match(Token.TokenType.IntLiteral));
                match(Token.TokenType.RightBracket);
                ArrayDecl ad = new ArrayDecl(v, t, i);
                result.Add(ad);
            }
            else
            {
                VariableDecl vd = new VariableDecl(v, t);
                result.Add(vd);
            }

            while (current_token.getType() == Token.TokenType.Comma)
            {
                match(Token.TokenType.Comma);
                Variable v1 = new Variable(match(Token.TokenType.Identifier));
                if (current_token.getType() == Token.TokenType.LeftBracket)
                {
                    match(Token.TokenType.LeftBracket);
                    int i = Convert.ToInt32(match(Token.TokenType.IntLiteral));
                    match(Token.TokenType.RightBracket);
                    ArrayDecl ad = new ArrayDecl(v1, t, i);
                    result.Add(ad);
                }
                else
                {
                    VariableDecl vd2 = new VariableDecl(v1, t);
                    result.Add(vd2);
                }
            }

            match(Token.TokenType.Semicolon);

            return result;
        }

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