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As shown in the figure the various logic gates have been mentioned.
Let the output before the NOT gate be Z.
Using the expression for the logic gates, it can be written
Z=(A+B)⋅(A⋅B)
Hence, the output Y is
Y=Z=(A+B)⋅(A⋅B)⇒Y=A⋅B
Hence the digital circuit is equivalent to an AND gate.