[Tex/LaTex] Shortest code causing “Emergency stop.” error

Question

This question is purely academic. TeXing a file containing

\valign{\halign#\cr!

causes an ! Emergency stop. error. Is that the shortest code which produces a fatal error in TeX?

Answer 1

\def\a{a\a}\a

EDIT: Shorter version, as suggested by Bruno:

\def~{~~}~

This gives I can't go on meeting you like this:

\halign{#&&#\cr\multispan{300}}

And this gives This can't happen:

\halign{#&&#\cr\multispan{300}\cr}