users on principle?

It looks to me as though my problem with browsing around

under http://plan9.bell-labs.com/sources/ (and other subpages)

is because the server doesn't like the User-Agent string:

$ telnet plan9.bell-labs.com 80
Trying 135.104.24.16...
Connected to plan9.bell-labs.com.
Escape character is '^]'.
GET /sources/contrib/ HTTP/1.1
Host: plan9.bell-labs.com
Connection: keep-alive
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.116 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
DNT: 1
Accept-Encoding: gzip, deflate, sdch
Accept-Language: en-US,en;q=0.8

HTTP/1.1 200 OK
Connection closed by foreign host.

And here it is again w/o the User-Agent string:

$ telnet plan9.bell-labs.com 80
Trying 135.104.24.16...
Connected to plan9.bell-labs.com.
Escape character is '^]'.
GET /sources/contrib/ HTTP/1.1
Host: plan9.bell-labs.com
Connection: keep-alive
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
DNT: 1
Accept-Encoding: gzip, deflate, sdch
Accept-Language: en-US,en;q=0.8

HTTP/1.1 200 OK
Server: Plan9
Date: Sun, 02 Oct 2016 17:29:09 GMT
Connection: close
Last-Modified: Fri, 14 Mar 2014 22:14:11 GMT
Content-Type: text/html

[... proper body returned...]

I tried playing around with the UA value and found that if I change
AppleWebKit to something else such as AppleWebKis I get a
response...

Jim