Both, your and Abigail-IIs solution will fail for duplicate elements (although I don't know whether that's a problem or not) :
#!/usr/bin/perl
use strict;
use warnings;
my @list = qw( 1 1 2 );
my %hash;
@hash{@list}=1;
delete $hash{$_} for (1..@list);
print "is sequence\n" unless %hash;
perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ; # The
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' # web