dired: launch program withou stalling emacs

[Alain Muls]

Hi

I am learning to use dired for file operations. I found out how to 
launch a program associated with the extension using eg

(require 'dired-x)
(setq dired-guess-shell-alist-user
      '(("\\.pdf$" "evince")))

The inconvenience of this is that I have to close the program before I 
can resume working in emacs. Is there a possibility to launch the 
pdfviewer evince and be able to work in emacs without closing the pdfviewer?

Tx/Alain