On the action of the Hua subgroups in special Moufang sets

摘要

We show that in a special Moufang set, either the root groups are elementary abelian 2-groups, or the Hua subgroup H (= the Cartan subgroup) acts "irreducibly" on U, i.e. the only non-trivial H-invariant subgroup of a root group normalized by H is the whole root group.