From: utzoo!decvax!cca!gwyn@Brl@sri-unix
Newsgroups: net.unix-wizards
Title: Re:  Library functions with non-integer return types
Article-I.D.: sri-unix.3341
Posted: Sat Sep 18 01:40:05 1982
Received: Wed Sep 22 10:38:09 1982

From:     Doug Gwyn 
Date:     15 Sep 82 5:34:54-EDT (Wed)
If you don't say "extern" then you haven't made a reference unless
you actually USE the routine.  e.g. in 

double	cos(), sin();

but you don't get these included by the linker unless you reference
them (or if something you reference references them, ... [closure]).

A nice feature is that the sin/cos routine source can include 
with no conflict.

In fact, this is one of the few reasons I know of for the continued
existence of the non-static/extern outer block declarations.