About yas / choose value

[Fab]

Hello,
If you test the code below, you will notice that there is a small problem: " / yas / text " what appears, what I do not want.
How to correct the code?
Thank you.

# -*- mode: snippet -*-
# name:ensemble
# key: ens
# --
${1:$$(yas/choose-value '("N" "Z" "D" "Q" "R"))}${1:$(yas/latex-choose-group yas/text)} $0

(defun yas/latex-choose-group (text)
  (cond ((string= text "N") "\$\\\mathbb{N}\$" )
        ((string= text "Z") "\$\\\mathbb{Z}\$" )
        ((string= text "D") "\$\\\mathbb{D}\$" )
        ((string= text "Q") "\$\\\mathbb{Q}\$" )  
        ((string= text "R") "\$\\\mathbb{R}\$" )))