ine addition for $n$-bit
binary numbers. Then encode the description of the four-bit adder in
Figure <a href="#4bit-adder-figure">4bit-adder-figure</a>, and pose the queries needed
to verify that it is in fact correct.


<figure>
  <img src="https://aimacode.github.io/aima-exercises/figures/4bit-adder.svg" alt="4bit-adder-figure" id="4bit-adder-figure" style="width:100%" />
  <figcaption><center><b>A four-bit adder. Each ${Ad}_i$ is a one-bit adder, as in figure <a class="insideExercisesFigRef" id="insidee