Defining 'not-last-page'

[Matthew Collett]

titling-init.ly contains the following definitions:

#(define (first-page layout props arg)
  (if (book-first-page? layout props)
      (interpret-markup layout props arg)
      empty-stencil))

#(define (last-page layout props arg)
  (if (book-last-page? layout props)
      (interpret-markup layout props arg)
      empty-stencil))

#(define (not-first-page layout props arg)
  (if (not (book-first-page? layout props))
      (interpret-markup layout props arg)
      empty-stencil))

Given these, it would seem to be trivial to complete the set by defining

#(define (not-last-page layout props arg)
  (if (not (book-last-page? layout props))
      (interpret-markup layout props arg)
      empty-stencil))

However, any attempt to _use_ this results in 'ERROR: Unbound variable: 
book-last-page?'.  This is extremely Schemely puzzling, since in exactly the 
same context 'last-page' works fine, even though it references the same 
putatively AWOL variable. For example,

\paper {
  oddHeaderMarkup = \markup { \fill-line {
    \null
    \fromproperty #'page:page-number-string
    {
      \on-the-fly #not-last-page { "More ..." }
      \on-the-fly #last-page { "No more." }
    }
  }}
  evenHeaderMarkup =  \oddHeaderMarkup
} 
\markup{}
\pageBreak
\markup{}

works as expected with the 'not-last-page' line commented out.  What is really 
going on here, and how can I get 'not-last-page' to work?

Best wishes,
Matthew