In the paper "[The display of a formal $p$-divisible group](https://smf.emath.fr/node/42448)" Zink defines some objects and calls them $3n$-display. A $3n$-display over $R$ is a quadruple $P$, $Q$, $F$, $F^1$ such that $P$ is a projective $W(R)$ module, $Q$ is a submodule and $F:P\to P$, $F^1 :Q\to P$ are functions satisfying some conditions. I don't know why these things are called $3n$-display and I don't see any relation to $3$ or $n$ in the definition. Does someone know the reason behind this name?



What is the reason behind the name 3n-display?
I have not found a source where Thomas Zink explains the name, however [arXiv:1906.00899](https://arxiv.org/abs/1906.00899) explains it as an abbreviation of *“not-necessarily-nilpotent”* (or $3n$-) displays. See also [Travaux de Zink](http://www.numdam.org/article/SB_2005-2006__48__341_0.pdf), page 343.


