[[!redirects Sandbox > history]] [[!redirects Sandbox]] < [[nlab:Sandbox]] completion of a ring Formal power series are more associated to geometry and analysis and topology than I thought. Adic topology, formal disks, formal spectra, et cetera there's a reason why the entire field of algebraic geometry exists. $R[x], R[x]/x^n R[x], R[[x]]$ Time to move out in the other direction, where we work in traditional mathematics. category: redirected to nlab