<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div><div><font face="Courier New">Here is a git diff of the proposed fix to the latest texbook.tex:</font></div><div><font face="Courier New"><br></font></div><div><font face="Courier New">$ git diff</font></div><div><font face="Courier New">diff --git a/tex/texbook/texbook.tex b/tex/texbook/texbook.tex</font></div><div><font face="Courier New">index a1e5078..54975e2 100644</font></div><div><font face="Courier New">--- a/tex/texbook/texbook.tex</font></div><div><font face="Courier New">+++ b/tex/texbook/texbook.tex</font></div><div><font face="Courier New">@@ -2956,7 +2956,7 @@ category~9 when |INITEX| begins.)</font></div><div><font face="Courier New"> characters, since the first |^^B| is converted to code~2 which doesn't</font></div><div><font face="Courier New"> equal the following character |^|. Hence</font></div><div><font face="Courier New"> the result is seven tokens: |^^B|$_7$ |^^B|$_7$</font></div><div><font face="Courier New">-|M|$_{11}$ \cstok{\^{}\^{}B} \]$_{10}$ |^^M|$_{11}$ \cstok{M\^{}\^{}M}.</font></div><div><font face="Courier New">+|M|$_{11}$ \cstok{\^{}\^{}B} |^^C|$_{10}$ |^^M|$_{11}$ \cstok{M\^{}\^{}M}.</font></div><div><font face="Courier New"> The last of these is a control word whose name has two letters.</font></div><div><font face="Courier New"> The \<space> after |\M| is deleted before \TeX\ inserts the \<return> token.</font></div></div><br id="lineBreakAtBeginningOfMessage"><br><blockquote type="cite">On Jul 22, 2024, at 2:25 PM, Hanson Char <hanson.char@gmail.com> wrote:<br><br class="Apple-interchange-newline">Hi,<br><br>I think I may have found an error in the answer of exercise 8.6 on page 305 of the TeXbook. <br><br><blockquote type="cite">EXERCISE 8.6<br>Assume that the category codes of plain TEX are in force, except that the characters<br>^^A, ^^B, ^^C, ^^M belong respectively to categories 0, 7, 10, and 11. What tokens are produced from the (rather ridiculous) input line ‘^^B^^BM^^A^^B^^C^^M^^@\M␣’? <br>(Remember that this line is followed by ⟨return⟩, which is ^^M; and recall that ^^@ denotes the ⟨null⟩ character, which has category 9 when INITEX begins.)<br></blockquote><br>The current answer says the result is seven tokens as follows: <br><br> ^^B_7 ^^B_7 M_11 ^^B ␣_10 ^^M_11 M^^M<br><br>But shouldn't it rather be:<br><br> ^^B_7 ^^B_7 M_11 ^^B ^^C_10 ^^M_11 M^^M<br><br>? Only the category code of ^^C is changed to 10, but the character code remains the same (ie 3).<br><br>Thoughts?<br><br>Regards,<br>Hanson</blockquote><br><br></body></html>