def solution(phone_book):
    answer = True
    
    phone_book = sorted(phone_book, key = lambda x : len(x))
    flag = 0
    while(phone_book) :
        temp = phone_book.pop(0)
        for i in phone_book :
            if temp in i[0:len(temp)] :
                answer = False
                flag = 1
                break
        if flag == 1 :
            break
    
    return answer