cell a {
    use bottom=first;
    box A;
    box B[size=40];
    box C,D;
    A->C;
    A->D [color=red];
}
below cell b {
    use bottom=first;
    box A;
    box B[size=40];
    box C, D;
    use routing.block_others=no;
    A->C;
    A->D [color=red];
}
