> I meant that there is a fundamental difference between a mere library
> alias and a library defined through a hypothetical "extend" library
> declaration:
>
> (define-library (srfi 158)
>    (extend (srfi 121))
>    (export make-accumulator ...)
>    (import (scheme base) ...)
>    (begin ...))

Oh yeah, it's true that an `extend` that can be combined with other
declarations has different semantics.

> Already implemented in Unsyntax. :) Basically just two lines of
> non-trivial code.

Nice, fast work!