@x=(\$_,\$_);
my $initial_value = $x[0];
$_=10;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
die "But \$x[0] did not change.\n" if $x[0] eq $initial_value;
$_=20;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
die "But \$x[0] did not change.\n" if $x[0] eq $initial_value;