If the two input of the NAND gates are joined to make one input as shown in Fig, then the NAND gate function as a NOT gate. As
`y=bar(A.A)=bar(A)+bar(A)=bar(A)`
In the truth table of NAND gate, if we use B=A, we obtain the truth table as given in Fig., which is the truth table of NOT gate.
`|(A,B=A,Y),(0,0,1),(1,1,0)|`
