# WRONG
        ...
        my $traverse;
        $traverse = sub {
                my(@c, $c, @m); 
                @c = $_[0];
                while (@c) {
                        $c = pop @c;
                        for (@{$member{$c}}) 
                                { push @m, $_; }
                        for (@{$child{$c}}) 
                                { push @c, $_; }
                }
                @m;
        };
        for (keys(%cut)) {
                my @m = &$traverse($_);
                my @m0 = grep { !$poison{$_} } @m;
                my @m1 = grep { $poison{$_} } @m;
                print "( ", jointab(@m0), "@ ", jointab(@m1), ")\n";
        }
        ...