Models of the Lie algebra F4

We describe the models of the exceptional Lie algebra F4 which are based on its semisimple subalgebras of rank 4. The underlying fact is that any reductive subalgebra of maximal rank of a simple Lie algebra induces a grading on this algebra by means of an abelian group, in such a way that the nontrivial components of the grading are irreducible modules.