can't get examples to work in .ly file

[Tim Righart]

> I am not top-posting

Dear developer,

With examples and tutorials found around the web i am managing to get some 
programming done in scheme for lilypond with one exception: I can't get the 
properties function to work and i can't see why. All scheme programming seems 
to 
work fine, as long as i'm not using properties. So this example works fine:

-- begin file --
#(define-markup-command (double-box layout props text) (markup?)
  "Draw a double box around text."
  (interpret-markup layout props
    (markup #:override '(box-padding . 0.4) #:box
            #:override '(box-padding . 0.6) #:box text)))
            
\markup \double-box A
-- end file --

But this example generates an error:

-- begin file --
#(define-markup-command (double-box layout props text) (markup?)
  #:properties ((inter-box-padding 0.4)
                (box-padding 0.6))
  "Draw a double box around text."
  (interpret-markup layout props
    (markup #:override `(box-padding . ,inter-box-padding) #:box
            #:override `(box-padding . ,box-padding) #:box text)))

\markup \double-box A
\markup \override #'(inter-box-padding . 0.8) \double-box A
\markup \override #'(box-padding . 1.0) \double-box A
 -- end file --

The error reported is: "Unbound variable: inter-box-padding"

I'm using windows 7 64 bit, lilypond 2.12.3

I hope you can tell me what i'm doing wrong

Best Regard, Tim