+ Book *b = unsmob<Book> (book);
+ return ly_is_module (b->header_) ? b->header_ : SCM_BOOL_F;
+}
+
+LY_DEFINE (ly_book_set_header_x, "ly:book-set-header!",
+ 2, 0, 0, (SCM book, SCM module),
+ "Set the book header.")
+{
+ LY_ASSERT_SMOB (Book, book, 1);
+ SCM_ASSERT_TYPE (ly_is_module (module), module, SCM_ARG2, __FUNCTION__,
+ "module");
+
+ Book *b = unsmob<Book> (book);
+ b->header_ = (module);
+ return SCM_UNSPECIFIED;