Es sei K {\displaystyle {}K} ein Körper. Vergleiche die beiden Ringe ( K [ X ] ) [ [ Y ] ] {\displaystyle {}(K[X])[\![Y]\!]} und ( K [ [ Y ] ] ) [ X ] {\displaystyle {}(K[\![Y]\!])[X]} .
![{\displaystyle {}(K[X])[\![Y]\!]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/ccbd6a84dad043daaa42bf930527c0a07da4d8da)
![{\displaystyle {}(K[\![Y]\!])[X]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/d5471cd569088a41efc8c21a971c65e89bdde70e)