I simply didn't remember how to use cons* ;-)
 

;; This is an operating system configuration template
;; for a "desktop" setup with GNOME and Xfce where the
;; root partition is encrypted with LUKS.

(use-modules (gnu) (gnu system nss))
;(use-modules (gnu packages tryton))
;(use-modules (gnu packages databases))
;(use-modules (gnu packages xorg))
(use-modules (gnu services xorg))
(use-service-modules desktop)
(use-package-modules certs gnome)
;(use-service-modules databases)

;(use-service-modules trytond)



(operating-system
  (host-name "antelope")
  (timezone "Europe/Paris")
  (locale "it_IT.utf8")

  ;;This is to be able to login into a guest system
  (kernel-arguments '("console=ttyS0"))
 
  ;; Assuming /dev/sdX is the target hard disk, and "my-root"
  ;; is the label of the target root file system.
  (bootloader (grub-configuration (target "/dev/sda")))

  (file-systems (cons (file-system
                        (device "my-root")
                        (title 'label)
                        (mount-point "/")
                        (type "ext4")
                      
                      )
                      %base-file-systems))

  (users (cons (user-account
                (name "catonano")
        (password (crypt " " "ab"))
                (comment "Alice's brother")
                (group "users")
                (supplementary-groups '("wheel" "netdev"
                                        "audio" "video"))
                (home-directory "/home/catonano"))
               %base-user-accounts))

 
  ;; This is where we specify system-wide packages.
  (packages (cons* nss-certs         ;for HTTPS access
                   gvfs              ;for user mounts
           ;;python-trytond
           ;;tryton
           ;;postgresql
                   %base-packages))

  ;; Add GNOME and/or Xfce---we can choose at the log-in
  ;; screen with F1.  Use the "desktop" services, which
  ;; include the X11 log-in service, networking with Wicd,
  ;; and more.      
 
  (services
 
   (cons*
    (service agetty-service-type
         (agetty-configuration (tty "ttyS0")))
    (gnome-desktop-service)
    (xfce-desktop-service)
    %desktop-services))
             
  ;; Allow resolution of '.local' host names with mDNS.
  (name-service-switch %mdns-host-lookup-nss))