Start
 -> tunnel ->
 End
 -> END
 
 == tunnel ==
 In tunnel.
 ->->
 
 === function function_to_evaluate() ===
     { zero_equals_(1):
         ~ return "WRONG"
     - else:
         ~ return "RIGHT"
     }
 
 === function zero_equals_(k) ===
     ~ do_nothing(0)
     ~ return  (0 == k)
 
 === function do_nothing(k)
     ~ return 0