public static IAggregateFluent<TNewResult> Lookup<TResult, TForeignDocument, TNewResult>(
	this IAggregateFluent<TResult> aggregate,
	IMongoCollection<TForeignDocument> foreignCollection,
	Expression<Func<TResult, Object>> localField,
	Expression<Func<TForeignDocument, Object>> foreignField,
	Expression<Func<TNewResult, Object>> as,
	AggregateLookupOptions<TForeignDocument, TNewResult> options = null
)

<ExtensionAttribute>
Public Shared Function Lookup(Of TResult, TForeignDocument, TNewResult) ( 
	aggregate As IAggregateFluent(Of TResult),
	foreignCollection As IMongoCollection(Of TForeignDocument),
	localField As Expression(Of Func(Of TResult, Object)),
	foreignField As Expression(Of Func(Of TForeignDocument, Object)),
	as As Expression(Of Func(Of TNewResult, Object)),
	Optional options As AggregateLookupOptions(Of TForeignDocument, TNewResult) = Nothing
) As IAggregateFluent(Of TNewResult)

[<ExtensionAttribute>]
static member Lookup : 
        aggregate : IAggregateFluent<'TResult> * 
        foreignCollection : IMongoCollection<'TForeignDocument> * 
        localField : Expression<Func<'TResult, Object>> * 
        foreignField : Expression<Func<'TForeignDocument, Object>> * 
        as : Expression<Func<'TNewResult, Object>> * 
        ?options : AggregateLookupOptions<'TForeignDocument, 'TNewResult> 
(* Defaults:
        let _options = defaultArg options null
*)
-> IAggregateFluent<'TNewResult>