def solution(phone_book):
phone_book.sort(key=lambda x:x)
# return phone_book
i = 0
while i < len(phone_book)-1: #for i in range(len(phone_book)-1):
k = len(phone_book[i])
for j in range(i+1, len(phone_book)):
if phone_book[j][:k] == phone_book[i]:
return False
elif len(phone_book[j])>k:
break
i += 1
return True