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Now, to illustrate the concept of
mutually recursive methods, suspend disbelief, and suppose that
you have decided that the rabbits method is too big. Accordingly,
you rewrite the rabbits method in terms of two auxiliary methods:
Integer method definition • instance rabbits (self = 0 or: [self = 1]) ifTrue: [^ 1] ifFalse: [^ self previousMonth + self penultimateMonth]
Realizing that previousMonth must answer the number of rabbits at
the end of the previous month, you see that you can define
previousMonth as follows:
Integer method definition • instance previousMonth ^ (self - 1) rabbits
Analogous reasoning leads you to the following definition for
penultimateMonth:
Integer method definition • instance penultimateMonth ^ (self - 2) rabbits