  Recently it has been shown that there exists a sector within the
Faddeev-Niemi model for which the equations of motion may be reduced to first
order equations. However, no solutions to that sector have been given. It is
not even known whether this sector contains topologically nontrivial solutions,
at all.
  Here, we show that two models with analytically known Hopf solitons, namely
the Nicole and the Aratyn-Ferreira-Zimerman models, possess sectors which can
be integrated to first order partial differential equations. The main result is
that these sectors are topologically nontrivial. In fact, all analytically
known hopfions belong to them.
