Constructing Recursive Data Structures

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With the previous characterization:

?- natural(z).
yes

?- natural(potato).
no

?- natural(s(s(s(z)))).
yes

?- natural(X).
X = z ;
X = s(z) ;
X = s(s(z));


?- natural(s(s(X))).
X = z ;
X = s(z) ;
X = s(s(z));