public static PipelineStageDefinition<TInput, TOutput> Lookup<TInput, TForeignDocument, TOutput>(
	IMongoCollection<TForeignDocument> foreignCollection,
	FieldDefinition<TInput> localField,
	FieldDefinition<TForeignDocument> foreignField,
	FieldDefinition<TOutput> as,
	AggregateLookupOptions<TForeignDocument, TOutput> options = null
)

Public Shared Function Lookup(Of TInput, TForeignDocument, TOutput) ( 
	foreignCollection As IMongoCollection(Of TForeignDocument),
	localField As FieldDefinition(Of TInput),
	foreignField As FieldDefinition(Of TForeignDocument),
	as As FieldDefinition(Of TOutput),
	Optional options As AggregateLookupOptions(Of TForeignDocument, TOutput) = Nothing
) As PipelineStageDefinition(Of TInput, TOutput)

static member Lookup : 
        foreignCollection : IMongoCollection<'TForeignDocument> * 
        localField : FieldDefinition<'TInput> * 
        foreignField : FieldDefinition<'TForeignDocument> * 
        as : FieldDefinition<'TOutput> * 
        ?options : AggregateLookupOptions<'TForeignDocument, 'TOutput> 
(* Defaults:
        let _options = defaultArg options null
*)
-> PipelineStageDefinition<'TInput, 'TOutput>