6

In the TeXbook, Knuth asks:

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
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    \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
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    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
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    @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
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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).

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