How to - simple process module in CRAM

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I am learning about CRAM designators and process modules. At this moment I am trying to create a stupid process module to check if I understand how the system works.

I am following http://ros.org/wiki/cram_process_modules (this tutorial) but I have not succeeded.

When I execute the following code:

CPL> (def-process-module navigation (input-designator)
          (let ((goal-pose (reference input-designator)))
            (or (execute-navigation-action goal-pose)
                (fail 'navigation-failed))))

An error is raised in SLIME:

The variable NAVIGATION is unbound.
    [Condition of type UNBOUND-VARIABLE]

I don't understand why this is happening. "Navigation" is the name of the process module I am trying to define, am I right? Therefore, I can understand an error raised because "execute-navigation-action" is not defined but not in "navigation". What I am missing?

Thanks in advance.