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4-bit Subtractor [TOC]
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A 4-bit adder does not compute not $a+b$ but actually $(a+b) mod 16$.
Regarding this arithmetic operation,  $G = \{0,1\}^4 $ forms a group. For each
$ a \in G$, there exists a unique inverse element $-a$ concerning addition, and
it satisfies the property $ a + (-a) = 0$ (where 0 denotes a bit pattern
consisting only of zeros).

The practical application is that subtraction can be reduced to addition. To
achieve this, it is only necessary to determine the corresponding bit pattern
of $b$ for any bit pattern $a$. One can easily derive a rule for this:
Adding the bit pattern `1111` to the bit pattern `0001` results in the bit
pattern `0000`. Adding the inverted bit pattern (in this case, `0101`) to a bit
pattern (for example, `1010`) always results in `1111`. If you additionally set
`Cin` to `1`, the result is always `0000`.

Task
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Implement a logic circuit for subtraction in CircuitVerse. Use a 4-bit wide NOT
gate to invert the bit pattern of $b$. Subtraction (analogous to addition)
will then calculate $ (a - b) \bmod 16 $, not $a - b$. Modify the circuit so
that `Cout` indicates `0` when $a - b = (a - b) \bmod 16$ holds. Otherwise,
`Cout` should have the value `1`.