Centuries ago, on Earth, mathematicians jokingly spoke of a researcher's "Erdős number"—their distance, in coauthorships, from the prolific Paul Erdős. More recently, anthropologists have taken to calculating one another's "Aran number".

At some point, some academic wit or another made the obvious point that, given the nature of her field work, one could calculate a different sort of Aran number: one's distance, in presence at planetary destructions, from a planet she destroyed. (She would protest that, on nearly every occasion, planets are destroyed near her, not by her, but deep in her heart she knows what a "proximate cause" is.) Because her field work is largely solitary, fewer beings have this sort of Aran number than the academic one, and the sets are nearly disjoint because few academics attend planetary destructions.