c:\test\546536>p1
print scalar keys %main::;; ## Before use POSIX main has how many globals?
67

use POSIX qw[ pow ];;

print scalar keys %main::;; ## and after is has
72
Terminating on signal SIGINT(2)

c:\test\546536>p1
$h{ $_ }++ for keys %main::;; ## Record what we have before

use POSIX qw[ pow ];;

$h{ $_ }++ for keys %main::;; ## Again after

print for grep{ $h{ $_ } == 1 } keys %h;;  ## Display the differences
_<c:/Perl/lib/auto/POSIX/POSIX.dll
XSLoader::
POSIX::
pow
_<POSIX.c