def __radiateDown(self, x1, x2, childId, condition) :
		"Radiates down: walks self.children downward until condition is no longer verifed or there's no childrens left "
		ret = []
		i = childId
		while 0 <= i :
			if condition(x1, x2, self.children[i]) :
				ret.append(self.children[i])
			else :
				break
			i -= 1
		return ret