already, yet

在美式英语里, already可用作an intensive [增强语气的词] after a word or phrase [短语] to express impatience [不耐烦]，比如Will you come in already?

Yet一般用在疑问句或否定句里，如(espressoenglish):
1. Have you bought the tickets yet?
2. Have you arranged a taxi yet?
3. Have you reserved the hotel room yet?
4. Have you packed the bags yet?
5. Yes, I've already bought the tickets.
6. Yes, I've already arranged a taxi.
7. No, I haven't reserved the room yet.
8. No, I haven't packed the bags yet.

LDOCE: 在yet another/more/bigger/higher等用法里，yet = still, used to emphasize [强调] that sth is even more than it was before or is in addition to what existed before:
9. He got a call from the lab, telling of yet more problems.
10. YACC stands for Yet Another Compiler Compiler. YACC provides a tool to produce a parser for a given grammar.

In spoken English, yet usually comes at句尾; In writing or more formal speech, yet can come after 'not', 例如We do not yet have a solution to this problem.