private function isColliding( a : GameObject, b : GameObject ) : Boolean
		{
			var collthreshSquared : Number = a.radius + b.radius;

			if ( collthreshSquared < Math.abs(a._position.x - b._position.x) )
				return false;

			if ( collthreshSquared < Math.abs(a._position.y - b._position.y) )
				return false;

			var atob : Vec2D = a._position.subtract( b._position );
			var lengthSquared : Number = atob.lengthSquared();
			collthreshSquared *= collthreshSquared;

			if ( lengthSquared > collthreshSquared )
			{
				return false;
			}

			return true;
		}