# Escaping the escape character

Exercise 7.2

Can you imagine why the designer of plain TeX decided not to make `\\` the control sequence for reverse slashes?

Is it something to do with the fact that control sequences formed by the escape character followed by a non-letter are control symbols and they expect a letter to follow?

• It's not a technical decision :-) – Joseph Wright Apr 20 '15 at 19:38
• `\answer` Reverse slashes (backslashes) are fairly uncommon in formulas or text, and `\\` is very easy to type; it was therefore felt best not to reserve `\\` for such limited use. Typists can define `\\` to be whatever they want (including `\backslash`). – egreg Apr 20 '15 at 19:45
• The TeXBook has answers to all questions at the end, you are allowed to look:-) – David Carlisle Apr 20 '15 at 20:04
• I should note that `\\` has a definition when Plain TeX starts off: `\meaning\\` prints `macro:#1pt->#1` – egreg Apr 20 '15 at 20:23
• @ShreevatsaR Yes, Knuth's very conservative and doesn't change things if not really needed. I seem to remember some place where the fact `\\` has a definition when `plain.fmt` is loaded has an unexpected consequence. – egreg Feb 9 '18 at 22:56

Knuth answers this in the TeXbook code (lines 2,300-2,305, or p 307):

``````\exercise Can you imagine why the designer of plain \TeX\ decided not
to make `|\\|' the control sequence for reverse slashes?^^{backslash}
\answer Reverse slashes (backslashes) are fairly uncommon in formulas or
text, and |\\| is very easy to type; it was therefore felt best not to
reserve |\\| for such limited use. Typists can define |\\| to be whatever
they want (including |\backslash|).
``````

or formatted:

Q: Can you imagine why the designer of plain TeX decided not to make `\\` the control sequence for reverse slashes?

A: Reverse slashes (backslashes) are fairly uncommon in formulas or text, and `\\` is very easy to type; it was therefore felt best not to reserve `\\` for such limited use. Typists can define `\\` to be whatever they want (including `\backslash`).