Flatten the sub-flows back into the super-flow by concatenating them. This is usually a bad idea when combined with GroupBy since it can easily lead to deadlock—the concatenation does not consume from the second substream until the first has finished and the GroupBy stage will get back-pressure from the second stream.

public virtual IFlow<TOut, TMat> ConcatSubstream()

abstract ConcatSubstream : unit -> IFlow<'TOut, 'TMat> 
override ConcatSubstream : unit -> IFlow<'TOut, 'TMat>