Questions about the library services during the Covid-19 measures

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Is the university library open?
Which regulations have to be observed when using the libraries on site?
Do I require a certificate for a test, vaccination or recovery to use the library?
Are there enough seats in the reading areas?
Are face masks required in the library?
What are the conditions for borrowing and returning?
Which library services help to use the university library from home?
Which virtual services are available?
Can I get literature that is not available at the University Library?
Can I get scans of print literature available at the Vienna University Library?