[metapost] subpath description in The METAFONTbook

Stephan Hennig mailing_list at arcor.de
Fri Mar 27 15:08:55 CET 2009

Taco Hoekwater schrieb:
> Stephan Hennig wrote:
>> around p.133, but this is probably in another edition:
>> <URL:http://books.google.de/books?q=subpath(t1,t2)>
> page 133, yes


> (the mfbook.tex is on CTAN, if you want to quote or paraphrase it)

Well, the incomplete description of subpath only came to my attention
when I was about to describe the precontrol and postcontrol operators.
In The MFbook Knuth only briefly referred to the description of subpath:

  precontrol t of p = last control point in subpath (0,t) of p
  postcontrol t of p = first control point in subpath (t,n) of p
  (plus two edge cases)

Unfortunately, while subpath works rather intuitively, any exhaustive
description of it is rather lengthy.  So either one has to insert a long
quote from The MFbook or add a reference to it (that was my spontaneous
idea).  But then, this sentence would no longer hold:

> Reading the manual does not require knowledge of \MF\ or
> access to {\sl The \MF book}, but both are beneficial.

Well, it never hold, but that would become more obvious with direct page
references to The MFbook.

To make references to The MFbook as convenient as possible for a reader
of mpman it would also seem more desirable to refer to lines in
mfbook.tex, since that is readily available on the net. But then we had
to make sure future changes to The MFbook do not break those references.
Don't really know how to handle this situation ...

Best regards,
Stephan Hennig

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