//Excerpt from visionary.C.

class not_enemy_of {
	const wabbit *const w;
	const unsigned radius;
public:
	not_enemy_of(const wabbit *initial_w, unsigned initial_radius)
		: w(initial_w), radius(initial_radius) {}

	//Return true if the other wabbit is not a nearby enemy of wabbit w.

	bool operator()(const wabbit *other) const {
		return other == w ||   //No animal is its own enemy.
			other->hungry() <= w->bitter() ||
			distance(w, other) > radius;
	}
};