酷暑だった夏もいつの間にか終わり、……（中略）……TeX 言語における「展開」に関する正しい理解は不可欠である。
というわけで、コレ。
この問題が悩まずにサラッと解けるようであれば、実用の TeX プログラミングについては十分な「展開力」を持っていると思っていいだろう。
解答集
この問題を Twitter 上で公開したところ、大勢（約 2 名）の人からの解答が得られた。
\def\withthreeargsexpanded#1#2#3#4{%
\def\xx@i{#2}\def\xx@ii{#3}\def\xx@iii{#4}%
%%% 63連
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter
\expandafter
#1%
%%% 63連
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter
\expandafter
{%
%%% 15連
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter
\expandafter
\xx@i
%%% 15連
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter
\expandafter
}%
%%% 15連
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter\expandafter\expandafter
\expandafter\expandafter
\expandafter
{%
%%% 3連
\expandafter\expandafter\expandafter
\xx@ii
%%% 3連
\expandafter\expandafter\expandafter
}%
%%% 3連
\expandafter\expandafter\expandafter
{%
\xx@iii
}%
}\expandafter マニアにはたまらないコードだね！
（コレはアレだ、という人は、もっと平凡な解答を自分で考えてみよう！）
（続く）
