How do you define a library?

I was thinking about this when I went onto 20Q, so I played with that in mind.
However at the end the computer told me that others had different ideas to me.

You were thinking of a library.
Could it be found in a classroom? You said Sometimes,
20Q was taught by other players that the answer is No.

Does it usually have four corners? You said Irrelevant,
20Q was taught by other players that the answer is Yes.

Is it tall? You said Irrelevant,
20Q was taught by other players that the answer is Yes.

Do you use it at night? You said Sometimes,
20Q was taught by other players that the answer is No.

Contradictions Detected
The opinions of the 20Q A.I. are its own, and are based on the input of players. 20Q's answers reflect common knowledge. If you feel that 20Q is in error, the only way to correct it is to play again!

So people,
computer literate people,
computer literate people who play with fun (but slightly intellectual) things on the web think...

That a library can't be found in a classroom.
That a library usually has four corners.
That a library is tall.
That you do not use a library at night.

Well, two out of those four things concern me slightly.