Erzwingende Algebra/Primäres Ideal/Induzierter Torsor/en/Fakt/Beweis

Beweis

We compute the cohomology class and the cohomology class given by the forcing algebra. For the first computation we look at the short exact sequence

On , the element is the image of (the non-zero entry is at the th place). The cohomology class is therefore represented by the family of differences

On the other hand, there are isomorphisms

The composition of two such isomorphisms on is the identity plus the same section as before.