<ExtensionAttribute()>
Public Overloads Shared Function ThenBy
    (Of TSource,TKey)( _
   ByVal source As IEntityQuery(Of TSource), _
   ByVal keySelector As Expression(Of Func(Of TSource,TKey)) _
) As IEntityQuery(Of TSource)

Dim source As IEntityQuery(Of TSource)
Dim keySelector As Expression(Of Func(Of TSource,TKey))
Dim value As IEntityQuery(Of TSource)
 
value = EntityQueryExtensions.ThenBy(Of TSource, TKey)(source, keySelector)

[ExtensionAttribute()]
public static IEntityQuery<TSource> ThenBy<TSource,TKey>( 
   IEntityQuery<TSource> source,
   Expression<Func<TSource,TKey>> keySelector
)

[ExtensionAttribute()]
public:
static IEntityQuery<TSource^>^ ThenBygeneric<typename TSource>
generic<typename TKey>
( 
   IEntityQuery<TSource^>^ source,
   Expression<Func<TSource^,TKey^>^>^ keySelector
) 

var mgr = new DomainModelEntityManager();

var query = mgr.Customers.OrderBy(c => c.Country).ThenBy(c => c.CompanyName);
var results = query.Execute();