on this SRFI there is code:

(define set-car+cdr!
  (lambda (p x y)
    (assert (pair? p))
    (perform
      (set-car! p x)
      (set-cdr! p y))))

But I can't find assert procedure anywhere, it's not in R7RS. I've only found
this SRFI but the name is test-assert in SRFI-64

https://srfi.schemers.org/srfi-64/srfi-64.html

So where this procedure is defined?

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Jakub T. Jankiewicz, Senior Front-End Developer
https://jcubic.pl/me