List<T> to IEnumerable<T> problem in interface
<pre><code>namespace WpfApplication3
{
public class Hex
{
    public String terr;
}    

public class HexC : Hex
{
    int Cfield;
}

public interface IHexGrid
{
    IEnumerable&lt;Hex&gt; hexs { get; }
}

public class hexGrid : IHexGrid //error CS0738: 'WpfApplication3.hexGrid' does not               
{
    public List&lt;Hex&gt; hexs { get; set; }
}

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        List&lt;HexC&gt; hexList1 = new List&lt;HexC&gt;();
        genmethod(hexList1); //but this compiles fine          
    }

    void genmethod(IEnumerable&lt;Hex&gt; hexList)
    {
        string str1;
        foreach (Hex hex in hexList)
            str1 = hex.terr;            
    }
}
}
</code></pre>

<p>The full error message is: 'WpfApplication3.hexGrid' does not implement interface member 'WpfApplication3.IHexGrid.hexs'. 'WpfApplication3.hexGrid.hexs' cannot implement 'WpfApplication3.IHexGrid.hexs' because it does not have the matching return type of 'System.Collections.Generic.IEnumerable'.</p>

<p>Why doesn't List implicitly cast to IEnumerable above? Thanks in advance!</p>
