For example when input terminals 530 and 531 are both at logical 0 state, {HEAD ~ the input} of {TAIL ~ NAND gate} 501 will both be at logic 1 state and line 537 will be at logical 0 state, which will be inverted to logic 1 state by inverter 511 at output terminal L0 
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For example when input terminals 530 and 531 are both at logical 0 state , { HEAD ~ the input } of { TAIL ~ NAND gate } 501 will both be at logic 1 state and line 537 will be at logical 0 state , which will be inverted to logic 1 state by inverter 511 at output terminal L0
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 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 OTH OTH OTH OTH OTH OTH