{
my $state = 'start';
my $crit = 3;

sub f_ab {
    my ($value) = @_;
    my $return = 0;

    if ($value >= $crit and $state ne 'high') {
        $state = 'high;
    }
    elsif ($value < $crit and $state ne 'low') {
        if ($state eq 'high) {
            $return = 1;
        }
        $state = 'low';
    }

    retrun $return;
}

}