The output of only one NAND gate will go to logical 0 state when both its input lines are at logic 1 state simultaneously, and so {HEAD ~ the outputs} of {TAIL ~ the remaining NAND gates} will be at logical 1 state 
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The output of only one NAND gate will go to logical 0 state when both its input lines are at logic 1 state simultaneously , and so { HEAD ~ the outputs } of { TAIL ~ the remaining NAND gates } will be at logical 1 state
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH