anchor.diff:  ----
   
   [source,c]
  -.foo.c
  +.`foo.c`
   ----
   
   #include "foo.h"
  
positive.code: which--not too surprisingly--has greetings as its main purpose. 
  
  [source,c]
  .foo.h
  ----
  #ifndef FOO_H
  #define FOO_H
  
negative.code: and test it using a quick C executable:
  
  [source,c]
  .`foo_test.c`
  ----
  #include "foo.h"
  
  