The Hasse-Witt matrix of a formal group
First, we shall define the Hasse-Witt matrix of a formal group. It is a natural lifting of the classical Hasse-Witt matrix. The classification up to isomorphism of smooth commutative formal groups is a matter of finding normal forms for the Hasse-Witt matrix of a formal group. Assuming the ground field to be algebraically closed, we shall derive some preliminary reductions for arbitrary dimension. Furthermore, we shall give intrinsic definitions for the discrete isomorphism invariants. The general results, together with the definitions of the discrete parameters, enable us to realize the covariant classification of two-dimensional smooth commutative formal groups in a way which is more transparent and needs less subcases than the combersome techniques of the book ''The covariant classification of two-dimensional smooth commutative formal groups over an algebraically closed field of positive characteristic'' by the author (Mathematical Centre Tracts 157, Amsterdam 1983; Zbl 0509.14050); chapter 2.
covariant classification of formal groups
scientific article; zbMATH DE number 3849406