I have this interface (simplified)

```
public interface IImageSourceViewModel : INotifyPropertyChanged
{
    /// <summary>
    /// Gets or sets the lines view model.
    /// </summary>
    IObservableCollection<ILine> LinesViewModel { get; set; }

 }

```

and I have this:

```
public class LineViewModel : PropertyChangedBase, ILine
{

}

```

and I implemented the interface as follow (Simplified):

```
public class ImageSourceViewModel : IImageSourceViewModel
{

      public IObservableCollection<LineViewModel> LinesViewModel { get; set; }
}

```

But I am getting error that LinesViewModel in implementation can not implement LinesViewModel in interface as it has a different return type. 

How can I fix this?