Missed some files.

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
+    {
+    }
+}