245: Mainline

Accordingly, you can solve the rabbits, previous_month, and penultimate_month ordering problem this way:

• First, supply a function prototype for rabbits. Because the function prototype has no body, there are no references to previous_month or to penultimate_month.
• Next, supply definitions for previous_month and penultimate_month. Both refer to rabbits, but those references are now harmless, because the rabbits function prototype is in place.
• Finally, supply a definition for rabbits. This definition includes calls to other functions, previous_month and penultimate_month, but those calls are harmless, because both functions have been defined.