[ESS] github flavor

[Stephen Bond]

Hello,

I am trying to activate the github flavor by:

(add-to-list 'auto-mode-alist
             '("\\.[rR]md\\'" . poly-gfm+r-mode))

as described in 
https://plantarum.ca/2021/10/03/emacs-tutorial-rmarkdown/

and get an error:
File mode specification error: (void-function poly-gfm+r-mode)

I have the following in my .emacs

(defun rmd-mode ()
  "ESS Markdown mode for rmd files"
  (interactive)
  ;; (setq load-path
  ;;   (append (list "path/to/polymode/" "path/to/polymode/modes/")
  ;;       load-path))
  (require 'poly-R)
  (require 'poly-markdown)     
  (poly-markdown+r-mode))
(add-to-list 'auto-mode-alist '("\\.md" . poly-markdown-mode))
(add-to-list 'auto-mode-alist '("\\.Snw" . poly-noweb+r-mode))
(add-to-list 'auto-mode-alist '("\\.Rnw" . poly-noweb+r-mode))
;; I commented out to emable gfm, markdown+r works
;;(add-to-list 'auto-mode-alist '("\\.Rmd" . poly-markdown+r-mode))
;; associate the new polymode to Rmd files:
(add-to-list 'auto-mode-alist
             '("\\.[rR]md\\'" . poly-gfm+r-mode))

(custom-set-variables
'(markdown-command
   (concat "pandoc" " --from=markdown --to=html" " --standalone --
mathjax --highlight-style=pygments"))
 '(org-agenda-files '("~/1.org"))
 '(package-selected-packages '(markdown-mode poly-R poly-markdown poly-
org polymode ess))
 '(poly-pandoc-exporter
   #s(pm-shell-exporter unbound "pandoc" nil nil nil pm-default-shell-
export-function pm-default-shell-export-sentinel nil)))

I am afraid there is a conflict somewhere.
Please, advise how to cleanup my setup.
Thanks
Stephen