You may well be right in which case I dont agree with the present framing of WPOR as its being applied to mathematics articles I dont consider it any more original research to invent an example like  than it is to invent a graphic showing the basic structure of a virus In any case Ive seen the example of the cooks and their measuring jugs elsewhere and it not infrequently appears in one form or another in IQtype tests so its not an invented example anyway But my fundamental position is that anyone who has followed the exposition of the algorithm to that point would have no difficulty in perceiving the truth of the statement so a citation would only be there to reassure those who havent understood whats been said Thats surely not the purpose of providing citations