Sub Articulo 77.3

One obvious simplification:
\def\obeylinesmode{\vbox\bgroup% Begin reading text
   \obeylines% or whatever
   \futurelet\next\lines}
\def\lines{\ifcat\bgroup\noexpand\next \let\next\llines
   \else\let\next\lnes\fi \next}
\def\llines{\bgroup\aftergroup\lllines\let\next}
\def\lnes{\lllines}
\def\lllines{\egroup}% Finally put it in the \vbox