public abstract Task<IAsyncCursor<TResult>> MapReduceAsync<TResult>(
	BsonJavaScript map,
	BsonJavaScript reduce,
	MapReduceOptions<TDocument, TResult> options = null,
	CancellationToken cancellationToken = null
)

Public MustOverride Function MapReduceAsync(Of TResult) ( 
	map As BsonJavaScript,
	reduce As BsonJavaScript,
	Optional options As MapReduceOptions(Of TDocument, TResult) = Nothing,
	Optional cancellationToken As CancellationToken = Nothing
) As Task(Of IAsyncCursor(Of TResult))

abstract MapReduceAsync : 
        map : BsonJavaScript * 
        reduce : BsonJavaScript * 
        ?options : MapReduceOptions<'TDocument, 'TResult> * 
        ?cancellationToken : CancellationToken 
(* Defaults:
        let _options = defaultArg options null
        let _cancellationToken = defaultArg cancellationToken null
*)
-> Task<IAsyncCursor<'TResult>>