Section Least.
Variables (T : finType) (F : {set T} -> {set T}).
Hypothesis (F_mono : {homo F : X Y / X \subset Y}).
Let n := #|T|.
Let iterF i := iter i F set0.
Definition fixset := iterF n.
Hint Resolve fixsetK : core.

Lemma fix_order_eq0 (x : T) : (fix_order x == 0) = (x \notin fixset).