Talk:Cumulative hierarchy

Sorry, function letter P in row 4 is undefined. I suppose it stands for 'power set of', but I am not a mathemetician, so I do not know. Anyhow, it would be better defining P or at least inserting a link to its explanation. Thanks — Preceding unsigned comment added by 188.6.77.5 (talk) 12:04, 22 September 2016 (UTC)