The second control signal is coupled to {TAIL ~ an input} of the NAND gate and inactivates {HEAD ~ the first control signal} 
The second control signal is coupled to { TAIL ~ an input } of the NAND gate and inactivates { HEAD ~ the first control signal }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD