Kernels in the category of formal group laws (Q2798989)

The goal of the paper is to provide an explicit construction of kernels in the category of formal group laws over a finite field \(k\) and the ring \(W\) of Witt vectors in terms of Dieudonné modules and Fontaine's triples, respectively. The author's approach overcomes the deficiency of implicit construction of Tate and Raynaud and, moreover, they deduce some well-known results in two important cases: homomorphisms between formal group laws of finite height and pure homomorphisms that are introduced within the scope of the paper. The dual problem related to explicit construction of cokernels in the same categories is left for future investigation. Like reasoning in the context of global extension enables the authors to establish the existence of a strict isomorphism between the formal norm torus and a formal group law coming from L-series.