How to use an inferior when input rewriting in GUIX?

The GUIX Inferiors manual states that > Thus you can insert an inferior package pretty much anywhere you > would insert a regular package: in manifests, in the packages field of > your operating-system declaration, and so on. However, I cannot figure out how to use an Inferior when rewriting the input of a package. E.g. this manifest, based on the Defining Package Variants section of the manual , does not work for me:

(use-modules (guix inferior) (guix channels) (guix packages)
             (srfi srfi-1))
(use-package-modules docker)
(use-package-modules python-xyz)

(define mychannels
  (list (channel
         (name 'guix)
         (url "https://git.savannah.gnu.org/git/guix.git ")
         ;; Last commit that still has python-pyyaml 5.4.1.
         (commit
          "d3e1a94391a838332b0565d56762a58cf87ac6b1"))))

(define myinferior
  (inferior-for-channels mychannels))

(define pyyaml5
  (first (lookup-inferior-packages myinferior "python-pyyaml")))


(define pyyaml5-instead-of-pyyaml6
  ;; This is a procedure to replace pyyaml 6.0 by pyyaml 5.4.1.

  ;; The line below does not work, raises this error:
  ;; In procedure package-properties: Wrong type argument:
  ;; #
  (package-input-rewriting `((,python-pyyaml . , pyyaml5)))

  ;; The line below does work (and has a similar result).
  ;(package-input-rewriting `((,python-pyyaml . , python-pyyaml-for-awscli)))
  )

(define docker-compose-with-pyyaml5
  (pyyaml5-instead-of-pyyaml6 docker-compose))

(packages->manifest
 (list pyyaml5
       (specification->package "python")
       docker-compose-with-pyyaml5
       ))

docker-compose only works with python-pyyaml 5.4.1 and the version in the channel has been upgraded to 6.0. The rewriting that I'm therefore trying to do is to rewrite the input to docker-compose to use python-pyyaml 5.4.1 from an earlier version of the channel. However, my attempts fail with

Backtrace:
In guix/packages.scm:
  1269:17 19 (supported-package? # …)
In guix/memoization.scm:
    101:0 18 (_ # # …)
In guix/packages.scm:
  1247:37 17 (_)
  1507:16 16 (package->bag _ _ _ #:graft? _)
  1608:48 15 (thunk)
  1403:25 14 (inputs _)
In srfi/srfi-1.scm:
   586:29 13 (map1 (("python-cached-property" #) …))
   586:29 12 (map1 (("python-distro" #) …))
   586:29 11 (map1 (("python-docker" #) …))
   586:29 10 (map1 (("python-dockerpty" #) …))
   586:29  9 (map1 (("python-docopt" #) …))
   586:29  8 (map1 (("python-dotenv" #) …))
   586:29  7 (map1 (("python-jsonschema" #) …))
   586:17  6 (map1 (("python-pyyaml" #) …))
In guix/packages.scm:
  1360:20  5 (rewrite ("python-pyyaml" #))
In guix/memoization.scm:
    101:0  4 (_ # # …)
In guix/packages.scm:
  1377:22  3 (_)
  1435:37  2 (loop #)
In ice-9/boot-9.scm:
  1685:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
In procedure package-properties: Wrong type argument: #

How can I do this rewriting of input with an inferior? Apparently there now is a python-pyyaml 5.4.1 in the channel, called python-pyyaml-for-awscli. Rewriting the input of docker-compose with that package does work as expected, so as far as I can see I'm using the correct syntax when rewriting input. (I'm not sure what the backtick, the dot, and the commas do, maybe there is a mistake there.) (As for the XY-problem, I can now run docker-compose using python-pyaml-for-awscli, however I'm still interested in how to use the Inferior, because next there might not be such a package available.)