IAggregateFluent<TNewResult> Lookup<TForeignDocument, TNewResult>(
	string foreignCollectionName,
	FieldDefinition<TResult> localField,
	FieldDefinition<TForeignDocument> foreignField,
	FieldDefinition<TNewResult> as,
	AggregateLookupOptions<TForeignDocument, TNewResult> options = null
)

Function Lookup(Of TForeignDocument, TNewResult) ( 
	foreignCollectionName As String,
	localField As FieldDefinition(Of TResult),
	foreignField As FieldDefinition(Of TForeignDocument),
	as As FieldDefinition(Of TNewResult),
	Optional options As AggregateLookupOptions(Of TForeignDocument, TNewResult) = Nothing
) As IAggregateFluent(Of TNewResult)

abstract Lookup : 
        foreignCollectionName : string * 
        localField : FieldDefinition<'TResult> * 
        foreignField : FieldDefinition<'TForeignDocument> * 
        as : FieldDefinition<'TNewResult> * 
        ?options : AggregateLookupOptions<'TForeignDocument, 'TNewResult> 
(* Defaults:
        let _options = defaultArg options null
*)
-> IAggregateFluent<'TNewResult>