Switch aa sw_3 '3' ZERO;
Switch ba sw_2 '2' ZERO;
Switch ca sw_1 '1' ZERO;
Switch da sw_0 '0' ZERO;

And ab sw_3 sw_c sw_d out3;
And bb sw_2 sw_c sw_d out2;
And cb sw_1 sw_c sw_d out1;
And db sw_0 sw_c sw_d out0;

Probe ac out3;
Probe bc out2;
Probe cc out1;
Probe dc out0;


Switch fa sw_c 'c' ZERO;
Switch fa sw_d 'd' ZERO;