"at the library" and "until" . (We usually don't use "till" in formal writing, but use it in speech. ) :)

As a U.S. native speaker, I feel that sentence as written by Kailin is correct and does not need to be changed. "At the library" is slightly more common but "in the library" is fine. There is nothing wrong with the word "till." It is not informal. It is not colloquial. It is actually older than "until." The American Heritage Dictionary says that "'Till' and 'until' are generally interchangeable in both writing and speech, though as the first word in a sentence until is usually preferred." "So remonstrance was impossible, and no steering could be done till the next varnishing day."--Lewis Carroll, "The Hunting of the Snark" "Then the light broke upon me, and I followed the two camels out of the Serai till we reached open road and the priest halted."--Rudyard Kipling, "The Man Who Would Be King" "Far along the world-wide whisper of the south-wind rushing warm, With the standards of the peoples plunging through the thunderstorm; Till the war-drum throbb'd no longer, and the battleflags were furl'd In the Parliament of man, the Federation of the world."--Tennyson, "Locksley Hall"

I vote for Ms Verna's answer. :-) Syed