 [semidet,multifile]try_proxy(+Proxy, 
+TargetAddress, -Socket, -StreamPair)Attempt a socket-level connection via the given proxy to
TargetAddress. The Proxy argument must match the 
output argument of proxy_for_url/3. 
The predicate tcp_connect/3 
(and http_open/3 from the
[semidet,multifile]try_proxy(+Proxy, 
+TargetAddress, -Socket, -StreamPair)Attempt a socket-level connection via the given proxy to
TargetAddress. The Proxy argument must match the 
output argument of proxy_for_url/3. 
The predicate tcp_connect/3 
(and http_open/3 from the library(http/http_open)) 
collect the results of failed proxies and raise an exception no proxy is 
capable of realizing the connection.
The default implementation recognises the values for Proxy 
described below. The library(http/http_proxy) adds
proxy(Host,Port) which allows for HTTP proxies using the
CONNECT method.
- direct
- Do not use any proxy
- socks(Host, Port)
- Use a SOCKS5 proxy