use strict;
use warnings;

my ($w, $x, $y, $z)=(undef,undef,7,7);

if ( equal( $x, $y ) ) {
	print "Equal\n";
} else {
	print "Not equal\n";
}

if ( equal( $w, $x ) ) {
	print "Equal\n";
} else {
	print "Not equal\n";
}

if ( equal( $y, $z ) ) {
	print "Equal\n";
} else {
	print "Not equal\n";
}

sub equal {
	my ( $first, $second ) = @_;
	local $^W;    # <  5.6
	no warnings;  # >= 5.6
	return $first == $second;
}