  Knapik et al. introduced the safety restriction which constrains both the
types and syntax of the production rules defining a higher-order recursion
scheme. This restriction gives rise to an equi-expressivity result between
order-n pushdown automata and order-n safe recursion schemes, when such devices
are used as tree generators. We show that the typing constraint of safety,
called homogeneity, is unnecessary in the sense that imposing the syntactic
restriction alone is sufficient to prove the equi-expressivity result for
trees.
