message: Another improvement
diff: @@ -434,7 +434,7 @@ where $p_0 - r_0$ is $2\ell + 1$ bits and $2^{\ell}(p_{10} - r_1)$ is $2\ell$ bi
  Firstly, if $p_0 - r_0$ created an underflow we would borrow from $p_1 - r_1$ by adding $2^{2\ell + 1}$ to $p_0 - r_0$ and subtracting $1$ from $p_1 - r_1$. However, recall that according to our definition of $u_0$, we already added to it the lowest $\ell$ bits of $p_1$ (i.e. $p_{10}$) and all of $r_1$. So, we've already added the bits we would borrow. Thus, no borrowing is needed here because it already implicitly accounted for.
  -Secondly, for $p_{10} - r_1$, we could borrow from $p_{11}$ or $p_2 - r_2$. This is the same as saying, we'd borrow from $p_{11} + p_2 - r_2 = u_1$. Thus, we would add $2^{2\ell}$ to $p_{10} - r_1$ and subtract $1$ from $u_1$. Thus, the constraint becomes
  +Secondly, if $p_{10} - r_1$ created an underflow, we would borrow from $p_{11}$ or $p_2 - r_2$. This is the same as saying, we'd borrow from $p_{11} + p_2 - r_2 = u_1$. Thus, we would add $2^{2\ell}$ to $p_{10} - r_1$ and subtract $1$ from $u_1$. Thus, the constraint becomes
  $$
  u_0 = 2^{\ell}(p_{10} - r_1) + p_0 - r_0 - c_0 \cdot 2^{2\ell}
  