PS One more argument for "define-auxiliary-syntax" is that it is the
more primitive construct vs. the magic module. Some later SRFI may
specify a general mechanism how to user-define auto-generated modules
(like the cxr or the auto module). In this case, the library (srfi 206
*) could be implemented through this mechanism and the primitive
"define-auxiliary-syntax". I think this is very much in line with the
Scheme philosophy.

(And for a general adapter macro translating between symbol keywords
to hygienic keywords in the sense of SRFI 177, we need the local
"define-auxiliary-syntax" anyway.)

Am Fr., 14. Aug. 2020 um 08:33 Uhr schrieb Marc Nieper-Wißkirchen
<xxxxxx@nieper-wisskirchen.de>:
>
> John, thank you very much for your comments.
>
> Am Fr., 14. Aug. 2020 um 04:41 Uhr schrieb John Cowan <xxxxxx@ccil.org>:
>
> > Suddenly you are talking about *equal* bindings, but until now (and in R[67]RS) it's about the bindings being the *same binding*.  That is, bound in one library (foo) and imported directly or indirectly from (foo) in all other libraries that use it.  Importing two libraries with *distinct* bindings is an error and is usually reported either by signaling an error or by reporting a warning.  It is not enough that the bindings are verbally identifiable: if (foo) defines `plus` with (define plus +) and (bar) does the same, then it is impossible to import both (foo) and (bar), because `plus` does not have the same binding in the two libraries.
>
> Technically, we are talking about equivalence in the sense of
> "free-identifier=?" of the appendix to R4RS and the R6RS standard
> libraries. I wanted to avoid this term, so I wrote just "equal
> binding" (in the sense of "same binding") but I will amend this as it
> obviously led to confusion.
>
> So, we are not inventing a third identifier equivalence (besides
> "free-identifier=?" and "bound-identifier=?") here, but we are just
> talking about the former. As you write, identifiers whose bindings
> refer to different locations, where just the stored values are
> equivalent (in the sense of "eq?", "eqv?" or "equal?") are not
> interesting.
>
> > This is why the (auto) library is good whereas the define-auxiliary-syntax macro is bad.  The library provides a single binding that all other libraries can import, and exactly how it is bound isn't important.  We have shown that it can be done with a simple syntax-rules definition, and anything fancier is just gravy.  Define-aux-syntax, though, attempts to introduce a novel (and unnecessary) notion of *equal* bindings, and should be left out altogether.
>
> This point does not apply as no novel equality is introduced here. I
> am sorry for the confusion and will amend the document accordingly.
>
> Actually, introducing the same binding (in the sense of
> "free-identifier=?") is nothing novel. Chez, for example, has the
> "alias" form, which exactly does this, namely giving an identifier the
> same binding as an existing identifier in scope. (It's a nice feature,
> which I have already used.)
>
> Operationally, in the expander model of Dybvig, two bound identifiers
> are "free-identifier=?" if and only if they have the same label.
>
> I hope this explanation helps to see that the local binding form
> "define-auxiliary-syntax" does no more magic than a local import of
> the magic "auto" library would do.