[texhax] Hyphenation questions

Philip TAYLOR P.Taylor at rhul.ac.uk
Sat Feb 4 00:18:37 CET 2012

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Doug McKenna wrote:

> I'd still like to understand what the definition of a duplicate
> hyphenation pattern is, other than "that which causes TeX to issue a
> particular error message".

TeX.web :

> @.Duplicate pattern@>
>   help1("(See Appendix H.)"); error;
>   end;

Appendix H, relevant part :

>  A hpatterni in the \patterns list has a more restricted form than a
> hwordi in the \hyphenation list, since patterns are supposed to be prepared
> by experts who are paid well for their expertise. Each hpatterni consists
> of one or more occurrences of hvalueihletteri, followed by hvaluei. Here hvaluei is either
> a digit (012 to 912) or empty; an empty hvaluei stands for zero. For example,
> the pattern `0a1b0' can be represented as 0a1b0 or a1b0 or 0a1b or simply
> a1b. A hletteri is a character token of category 11 or 12 whose \lccode is
> nonzero. If you want to use a digit as a hletteri, you must precede it by a nonempty
> hvaluei; for example, if for some reason you want the pattern `1a012' you can obtain
> it by typing `1a012', assuming that \lccode`1 is nonzero. Exception: The character
> `.' is treated as if it were a hletteri of code 0 when it appears in a pattern.
> Code 0 (which obviously cannot match a nonzero \lccode) is used by TEX to
> represent the left or right edge of a word when it is being hyphenated.

(funny characters courtesy of PDF copy-and-paste)

No mention of "duplicate" as far as I can see,
Why not assume that "duplicate" means "identical" ?
It probably does !

Philip Taylor
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