By Annette Huber, Guido Kings and Niko Naumann. Compositio Mathematica147,235–262. Definition2.1.1, printed p236, states filtration and p-valuation axioms; section2.2 gives formal-group examples. Publisher full text: www.cambridge.org/core/services/aop-cambridge-core/content/view/60EA940F508F25A61A13990CF91F27BE/S0010437X10004884a.pdf/some-complements-to-the-lazard-isomorphism.pdf