Covariant Honda theory
To every formal group \(F\), Honda in 1970 attached a matrix called (left) type to explicitly describe \(F\). Here the author attaches to each \(F\) another matrix (called right type) over the noncommutative twisted power series ring \(E\), which is connected with the reduction of \(F\), where \(F\) is over \(k\) and \(\mathcal{O}\), a perfect field with char \(k=p\neq 0\) and its ring of Witt vectors. An analogue of the Dieudonné module is constructed, and equivalence between the categories of formal groups and (certain) right modules is established. As an application, the \( \star \)-isomorphism classes of the deformations of a formal group and the action of its automorphism group on these classes are studied.
scientific article; zbMATH DE number 5001912