Programming with CLP($\Re$) (I)

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The folowing simple, recursive program defines the natural numbers:

nat(0).
nat(N):- N > 0, nat(N-1).
(zero is a natural number, and a number greater than zero is also a natural number, provided that its predecessor is a natural number)

?- nat(X).
X = 0 ;
X = 1 ;
X = 2 ;

?- nat(3.4).
no

?- nat(-8).
no

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The above definition can also be written as

nat(0).
nat(N + 1):- N >= 0, nat(N).
and works exactly in the same way