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In the Internet or On the internet

Which one I should use?
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Comments  (Page 2) 
Yeah, technically the Internet is a kind of internet (or as we'd say "an instance" of :)). There can be other internets. See https://en.wikipedia.org/wiki/Capitalization_of_%22Internet%22
Here is the most complete technical definition and description of the terms: Internet and internet. It even mentions the related term: intranet.
http://www.yourdictionary.com/internet

However, it erred in the acronym "IP", defining it as Internal Protocol, when it really is Internet Protocol. Here is a good definition and description of TCP/IP, which is the basic block of information transfer in the Internet.

http://searchnetworking.techtarget.com/definition/TCP-IP
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And what about "at the internet"?
Does the Internet exist in one place that you can visit?

eg.
Meet me at Women's Hospital.
You will find that book at the local bookstore.