Missed some files.

NTwain/IMemoryManager.cs

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+using System;
+namespace NTwain
+{
+    /// <summary>
+    /// Interface that provides the correct methods for managing memory on data exchanged with TWAIN sources.
+    /// </summary>
+    public interface IMemoryManager
+    {
+        /// <summary>
+        /// Function to allocate memory. Calls to this must be coupled with <see cref="MemFree"/> later.
+        /// </summary>
+        /// <param name="size">The size in bytes.</param>
+        /// <returns>Handle to the allocated memory.</returns>
+        IntPtr MemAllocate(uint size);
+
+        /// <summary>
+        /// Function to free memory. 
+        /// </summary>
+        /// <param name="handle">The handle from <see cref="MemAllocate"/>.</param>
+        void MemFree(IntPtr handle);
+
+        /// <summary>
+        /// Function to lock some memory. Calls to this must be coupled with <see cref="MemUnlock"/> later.
+        /// </summary>
+        /// <param name="handle">The handle to allocated memory.</param>
+        /// <returns>Handle to the lock.</returns>
+        IntPtr MemLock(IntPtr handle);
+
+        /// <summary>
+        /// Function to unlock a previously locked memory region.
+        /// </summary>
+        /// <param name="handle">The handle from <see cref="MemLock"/>.</param>
+        void MemUnlock(IntPtr handle);
+    }
+}

NTwain/ITwainOperation.cs

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+using NTwain.Data;
+using NTwain.Triplets;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace NTwain
+{
+    /// <summary>
+    /// Interface for providing TWAIN triplet operations. 
+    /// </summary>
+    public interface ITwainOperation
+    {
+        /// <summary>
+        /// Gets the triplet operations defined for audio data group.
+        /// </summary>
+        DGAudio DGAudio { get; }
+
+        /// <summary>
+        /// Gets the triplet operations defined for control data group.
+        /// </summary>
+        DGControl DGControl { get; }
+
+        /// <summary>
+        /// Gets the triplet operations defined for image data group.
+        /// </summary>
+        DGImage DGImage { get; }
+    }
+
+    /// <summary>
+    /// Internal interface for operations use.
+    /// </summary>
+    interface ITwainOperationInternal : ITwainOperation
+    {
+    }
+}

NTwain/TwainSessionBase.cs

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+using NTwain.Data;
+using NTwain.Triplets;
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Text;
+
+namespace NTwain
+{
+    public class TwainSessionBase : ITwainStateInternal, ITwainOperationInternal
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="TwainSession" /> class.
+        /// </summary>
+        /// <param name="appId">The app id.</param>
+        /// <exception cref="System.ArgumentNullException"></exception>
+        public TwainSessionBase(TWIdentity appId)
+        {
+            if (appId == null) { throw new ArgumentNullException("appId"); }
+            AppId = appId;
+            State = 1;
+            EnforceState = true;
+        }
+
+
+        #region ITwainStateInternal Members
+
+        /// <summary>
+        /// Gets or sets a value indicating whether calls to triplets will verify the current twain session state.
+        /// </summary>
+        /// <value>
+        ///   <c>true</c> if state value is enforced; otherwise, <c>false</c>.
+        /// </value>
+        public bool EnforceState { get; set; }
+
+        void ITwainStateInternal.ChangeState(int newState, bool notifyChange)
+        {
+            State = newState;
+            if (notifyChange)
+            {
+                RaisePropertyChanged("State");
+                OnStateChanged();
+            }
+        }
+
+        ICommitable ITwainStateInternal.GetPendingStateChanger(int newState)
+        {
+            return new TentativeStateCommitable(this, newState);
+        }
+
+        void ITwainStateInternal.ChangeSourceId(TWIdentity sourceId)
+        {
+            SourceId = sourceId;
+            RaisePropertyChanged("SourceId");
+            OnSourceIdChanged();
+        }
+
+        #endregion
+
+        #region ITwainState Members
+
+        /// <summary>
+        /// Gets the app id used for the session.
+        /// </summary>
+        /// <value>
+        /// The app id.
+        /// </value>
+        public TWIdentity AppId { get; private set; }
+
+        /// <summary>
+        /// Gets the source id used for the session.
+        /// </summary>
+        /// <value>
+        /// The source id.
+        /// </value>
+        public TWIdentity SourceId { get; private set; }
+
+        /// <summary>
+        /// Gets the current state number as defined by the TWAIN spec.
+        /// </summary>
+        /// <value>
+        /// The state.
+        /// </value>
+        public int State { get; private set; }
+
+        #endregion
+
+        #region ITwainOperation Members
+
+        DGAudio _dgAudio;
+        /// <summary>
+        /// Gets the triplet operations defined for audio data group.
+        /// </summary>
+        public DGAudio DGAudio
+        {
+            get
+            {
+                if (_dgAudio == null) { _dgAudio = new DGAudio(this); }
+                return _dgAudio;
+            }
+        }
+
+        DGControl _dgControl;
+        /// <summary>
+        /// Gets the triplet operations defined for control data group.
+        /// </summary>
+        public DGControl DGControl
+        {
+            get
+            {
+                if (_dgControl == null) { _dgControl = new DGControl(this); }
+                return _dgControl;
+            }
+        }
+
+        DGImage _dgImage;
+        /// <summary>
+        /// Gets the triplet operations defined for image data group.
+        /// </summary>
+        public DGImage DGImage
+        {
+            get
+            {
+                if (_dgImage == null) { _dgImage = new DGImage(this); }
+                return _dgImage;
+            }
+        }
+
+        #endregion
+
+        #region ITwainOperationInternal Members
+
+        #endregion
+
+        #region INotifyPropertyChanged Members
+
+        /// <summary>
+        /// Occurs when a property value changes.
+        /// </summary>
+        public event PropertyChangedEventHandler PropertyChanged;
+
+        /// <summary>
+        /// Raises the <see cref="PropertyChanged"/> event.
+        /// </summary>
+        /// <param name="propertyName">Name of the property.</param>
+        protected void RaisePropertyChanged(string propertyName)
+        {
+            var hand = PropertyChanged;
+            if (hand != null) { hand(this, new PropertyChangedEventArgs(propertyName)); }
+        }
+
+        #endregion
+
+        #region custom events and overridables
+
+        /// <summary>
+        /// Called when <see cref="State"/> changed.
+        /// </summary>
+        protected virtual void OnStateChanged() { }
+
+        /// <summary>
+        /// Called when <see cref="SourceId"/> changed.
+        /// </summary>
+        protected virtual void OnSourceIdChanged() { }
+
+
+        #endregion
+    }
+}