(a), (b). As suggested, we note that all single sentence symbol formulas have $4k+1$ symbols, where $k=0$ , at the same time having $k+1$ sentence symbols. Suppose, that two wffs $\alpha$ and $\beta$ have lengths $4k+1$ and $4m+1$ , and $k+1$ and $m+1$ sentence symbols, correspondingly. Then $\mathcal{E}_{\square}(\alpha,\beta)$ has length $4k+1+4m+1+3=4(k+m+1)+1$ and $k+1+m+1=(k+m+1)+1$ sentence symbols. Hence, by induction, any construction sequence leading to a well-formed formula that does not contain the negation symbol, ends up at an expression having length $4n+1$ with $n+1>\frac{4n+1}{4}$ sentence symbols.