diff --git a/.gitignore b/.gitignore
index 4a3a6d3..6c1ac87 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,9 @@
 ##
 ## Get latest from https://github.com/github/gitignore/blob/main/VisualStudio.gitignore
 
+# User-spacific editor config
+.editorconfig
+
 # User-specific files
 *.rsuser
 *.suo
diff --git a/MCTG/MCTGApp/MCTGApp.csproj b/MCTG/MCTGApp/MCTGApp.csproj
index f184388..79a52db 100644
--- a/MCTG/MCTGApp/MCTGApp.csproj
+++ b/MCTG/MCTGApp/MCTGApp.csproj
@@ -7,6 +7,10 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
+  <ItemGroup>
+    <None Include="..\.editorconfig" Link=".editorconfig" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\MCTGLib\MCTGLib.csproj" />
   </ItemGroup>
diff --git a/MCTG/MCTGApp/Program.cs b/MCTG/MCTGApp/Program.cs
index eb783ba..021e938 100644
--- a/MCTG/MCTGApp/Program.cs
+++ b/MCTG/MCTGApp/Program.cs
@@ -8,6 +8,7 @@ Console.WriteLine("Hello, World!\n");
 
 // TESTS:
 
+// tests on Recipe class
 BaseItem r1 = new Recipe("A recipe...");
 
 r1.DisplayItem();
@@ -16,6 +17,7 @@ r1.DisplayDescription();
 
 Console.WriteLine();
 
+// tests on RecipeCollection class
 RecipeCollection rc = new RecipeCollection("A recipe collection...");
 for (uint i = 0; i < 10; i++)
 {
@@ -24,16 +26,24 @@ for (uint i = 0; i < 10; i++)
 
 try // test overload of [] operator
 {
-    rc[1003].DisplayItem();
-    rc[2003].DisplayItem(); // incorrect index
+    rc[2].DisplayId();
+    rc.GetById(1002);
 }
 catch (ArgumentNullException)
 {
     Console.Error.WriteLine("An index are incorrect!\n");
 }
 
+// test of multiple params constructor
+RecipeCollection rc2 = new RecipeCollection(
+    new Recipe(),
+    new Recipe(),
+    new Recipe(),
+    new Recipe(),
+    new Recipe());
 
-foreach (Recipe r in rc.Collection)
+// test of Enumerable property
+foreach (Recipe r in rc2)
 {
     r.DisplayId();
     r.DisplayDescription();
diff --git a/MCTG/MCTGLib/BaseItem.cs b/MCTG/MCTGLib/BaseItem.cs
index 36a653c..f031d66 100644
--- a/MCTG/MCTGLib/BaseItem.cs
+++ b/MCTG/MCTGLib/BaseItem.cs
@@ -1,5 +1,6 @@
 
 using System;
+using System.ComponentModel;
 
 namespace Model
 {
@@ -7,24 +8,29 @@ namespace Model
     /// Define the base structure of any Items.<br/>
     /// An Item can be identifed and have a short description. It can also be displayed.
     /// </summary>
-    public abstract class BaseItem : IDisplayable
+    public abstract class BaseItem : IDisplayable, IEquatable<BaseItem>
     {
         /// <summary>
         /// The identifier of an Item.<br/>
         /// The first number correspond to the typs of the Item.
         /// </summary>
-        public uint Id { get; }
+        virtual public uint Id
+        {
+            get => _id;
+            init => _id = value;
+        }
+        protected uint _id;
+        
 
         /// <summary>
         /// A short description of the Item. Useful to know what this Item stand for.
         /// </summary>
         public string Description { get; set; }
+   
 
-
-        protected BaseItem(uint id, string description = "")
+        protected BaseItem(uint id, string description="Any Item.")
         {
-            Id = id;
-            Description = description;
+            Id = id; Description = description;
         }
 
 
@@ -52,5 +58,28 @@ namespace Model
         {
             Console.WriteLine(this.ToString());
         }
+
+        // IEquatable<BaseItem> implementation
+        public bool Equals(BaseItem? other)
+        {
+            if (other != null)
+                return this.Id.Equals(other.Id);
+
+            return false;
+        }
+
+        public override bool Equals(object? obj)
+        {
+            BaseItem? baseItem = obj as BaseItem;
+            if (baseItem == null) return false;
+            if (baseItem == this) return true;
+
+            return this.Id.Equals(baseItem.Id);
+        }
+
+        public override int GetHashCode()
+        {
+            return this.Id.GetHashCode();
+        }
     }
 }
diff --git a/MCTG/MCTGLib/Recipe.cs b/MCTG/MCTGLib/Recipe.cs
index 0e6611f..2ab5420 100644
--- a/MCTG/MCTGLib/Recipe.cs
+++ b/MCTG/MCTGLib/Recipe.cs
@@ -5,35 +5,68 @@ namespace Model
 {
     /// <summary>
     /// A Recipe is a description of step and maybe some techniques, with an ingredient list to make a meal.<br/>
-    /// It is instantiated with a new unique four digit id, where the first one is 1.
+    /// It is instantiated with a new unique id, where the first number is 1.
     /// </summary>
     public class Recipe : BaseItem
     {
-        /// <summary>
-        /// This static atrribute stand for the creation of a new id. It is incremented each time a new Recipe is instantiated.
-        /// </summary>
-        public static uint idIterator = 0;
+        #region Private Attributes
+
+        private static uint _idCreator = 0; // stand for the creation of a new id. It is incremented each time a new Recipe is instantiated.
+        private string title = "";
+
+        #endregion
+
+        #region Public Properties
 
         /// <summary>
         /// The title of the recipe.
         /// </summary>
-        public string Title { get; set; }
+        public string Title
+        {
+            get => title;
+            set
+            {
+                title = value;
+                if (string.IsNullOrEmpty(title)) title = $"Recipe n{this.Id}";
+            }
+        }
 
         /// <summary>
         /// All the details about the preparation of the meal.
         /// </summary>
         public string Preparation { get; set; }
 
+        #endregion
 
-        public Recipe(string description = "", string title = "", string preparation = "")
-            : base(idIterator+1000, description)
+        #region Constructors
+
+        public Recipe(string title="", string preparation="")
+            : base(ComputeId(), "A recipe.")
         {
-            if (idIterator == 1000) throw new OverflowException("id has reach the maximum value.");
             Title = title;
             Preparation = preparation;
-            idIterator++;
         }
 
+        #endregion
+
+        #region Private Methods
+
+        /// <summary>
+        /// Processi the unique identificator of an Item. The identificator is calculated to put the number representing
+        /// the type of item before the number of its number in its type.
+        /// </summary>
+        private static uint ComputeId()
+        {
+            uint dec = 0, id = _idCreator;
+            while ((_idCreator / (Math.Pow(10, dec)) > 10)) dec++;
+            id += 1 * (uint)(Math.Pow(10, dec));
+
+            return id;
+        }
+
+        #endregion
+
+        #region Public Methods
 
         public override string ToString()
         {
@@ -43,5 +76,7 @@ namespace Model
                 $"\t.Description  -  {Description}\n" +
                 $"______\n\n";
         }
+
+        #endregion
     }
 }
diff --git a/MCTG/MCTGLib/RecipeCollection.cs b/MCTG/MCTGLib/RecipeCollection.cs
index 594ae91..f93227d 100644
--- a/MCTG/MCTGLib/RecipeCollection.cs
+++ b/MCTG/MCTGLib/RecipeCollection.cs
@@ -1,38 +1,66 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 
 namespace Model
 {
     /// <summary>
     /// A Recipe collection is a group of recipe.<br/>
-    /// It is instantiated with a new unique four digit id, where the first one is 2.
+    /// It is instantiated with a new unique id, where the first number is 2.
     /// </summary>
-    public class RecipeCollection : BaseItem
+    public class RecipeCollection : BaseItem, ICollection<Recipe>
     {
-        /// <summary>
-        /// This static atrribute stand for the creation of a new id. It is incremented each time a new RecipeCollection is instantiated.
-        /// </summary>
-        private static uint idIterator = 0;
+        #region Private Attributes
+
+        private const int CAT_ITEM = 2;                             // the first number of the item full id : the item category.
+        private static uint _idCreator = 0;                         // stand for the creation of a new id. It is incremented each time a new Recipe is instantiated.
+        private ICollection<Recipe> _recipes = new List<Recipe>();  // main composent of this class.
+
+        #endregion
 
-        /// <summary>
-        /// The main composent of a RecipeCollection. This contain the Recipes included in this collection.
-        /// </summary>
-        public List<Recipe> Collection { get; set; }
 
+        #region Public Properties
+        #region ICollection Implementation
 
-        public RecipeCollection(string description = "", List<Recipe>? collection = null)
-            : base(idIterator + 2000, description)
+        public int Count => _recipes.Count;
+        public bool IsReadOnly => false;
+
+        #endregion
+        #endregion
+
+        #region Constructors
+
+        public RecipeCollection(string description="A recipe collection.")
+            : base(ComputeId(), description)
+        { }
+
+        public RecipeCollection(params Recipe[] recipes)
+            : base(ComputeId())
         {
-            if (idIterator == 1000) throw new OverflowException("id has reach the maximum value.");
+            _recipes.CopyTo(recipes, 0);
+        }
+
+        #endregion
 
-            if (collection == null)
-                Collection = new List<Recipe>();
-            else
-                Collection = collection;
+        #region Private Methods
 
-            idIterator++;
+        /// <summary>
+        /// Processi the unique identificator of an Item. The identificator is calculated to put the number representing
+        /// the type of item before the number of its number in its type.
+        /// </summary>
+        private static uint ComputeId()
+        {
+            uint dec = 0, id = _idCreator;
+            while ((_idCreator / (Math.Pow(10, dec)) > 10)) dec++;
+            id += CAT_ITEM * (uint)(Math.Pow(10, dec));
+
+            return id;
         }
 
+        #endregion
+
+        #region Public Methods
 
         public override string ToString()
         {
@@ -43,22 +71,66 @@ namespace Model
                 $"______\n\n";
         }
 
+        public Recipe GetById(uint id)
+        {
+            if (this._recipes is not List<Recipe>)
+                throw new InvalidCastException("Need to verify the type of the private attribute '_recipes'.");
+
+            return (this._recipes as List<Recipe>).Find(x => x.Id.Equals(Id));
+        }
+
+        #region ICollection Implementation
+
+        public void Add(Recipe item)
+        {
+            _recipes.Add(item);
+        }
+
+        public void Clear()
+        {
+            _recipes.Clear();
+        }
+
+        public bool Contains(Recipe item)
+        {
+            return _recipes.Contains(item);
+        }
+
+        public void CopyTo(Recipe[] array, int arrayIndex)
+        {
+            _recipes.CopyTo(array, arrayIndex);
+        }
+
+        public bool Remove(Recipe item)
+        {
+            return _recipes.Remove(item);
+        }
+
+        public IEnumerator<Recipe> GetEnumerator()
+        {
+            return _recipes.GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return _recipes.GetEnumerator();
+        }
+
+        #endregion
+
+        #endregion
+
+        #region Operators Overloading
+
         /// <summary>
         /// Overload the [] operator to access the Recipe directly without passing by the Collection.<br/>
         /// It use the identifier of the Recipe to get the item.
         /// </summary>
         /// <param name="id">The id of the Recipe</param>
         /// <returns></returns>
-        public Recipe this[uint id]
+        public Recipe this[Index id]
         {
-            get
-            {
-                foreach (Recipe r in this.Collection)
-                {
-                    if (r.Id == id) return r;
-                }
-                throw new ArgumentNullException("The id given dosen't correspond to any recipes in the collection.");
-            }
+            get => this.ElementAt(id);
         }
 
         /// <summary>
@@ -69,7 +141,7 @@ namespace Model
         /// <returns>The recipe collection where the recipe is added.</returns>
         public static RecipeCollection operator + (RecipeCollection coll, Recipe ri)
         {
-            coll.Collection.Add(ri); return coll;
+            coll.Add(ri); return coll;
         }
 
         /// <summary>
@@ -80,7 +152,9 @@ namespace Model
         /// <returns>The recipe collection where the recipe is removed.</returns>
         public static RecipeCollection operator - (RecipeCollection coll, Recipe ri)
         {
-            coll.Collection.Remove(ri); return coll;
+            coll.Remove(ri); return coll;
         }
+
+        #endregion
     }
 }