Here is a situation that I have been brewing over.

You want to set even characters in a stream to upper case and the others to odd.
You do not want to write new node code.
You have these ready made node programs:
  Switch everything to upper case,
  Switch everything to lower case,
  Send alternate incoming characters to two alternate output streams,
  Mesh two streams into one, taking alternate characters from alternate input streams.
Can you string these together to do the job?

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My current favorite plan is that no stream elements arrive without an invitation.
A buffer node is in a position to send out invitations up to its remaining capacity.
It is in a position to respond to down stream invitations with traffic.
I am vague on what strategy is uses to improve the world.
The edge output arcs of the graph of nodes send invitations for traffic as they are in a position.

I think that the arcs of new nodes come into existence with an invitation assumed.