Switch aa sw0 '0' ZERO;
Switch ba sw1 '1' ZERO;
Switch ca sw2 '2' ZERO;
Switch da sw3 '3' ZERO;
Switch ea sw4 '4' ZERO;
Switch fa sw5 '5' ZERO;
Switch ga sw6 '6' ZERO;
Switch ha sw7 '7' ZERO;

And ab-bb sw0 sw1  x0;
And cb-db sw2 sw3  x0;
And eb-fb sw4 sw5  x1;
And gb-hb sw6 sw7  x1;

Or  cc-fc  x0 x1  out;

Probe  cd-fd out;