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  1. longitud([], 0).
  2. longitud([X|Xs], N) :- longitud(Xs, N1), N is N1 + 1.
  3.  
  4. ?- longitud([2,4,6,8], X), write('longitud: '), writeln(X).
Success #stdin #stdout #stderr 0.02s 7740KB
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stdin
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Standard input is empty
stdout
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longitud: 4
stderr
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Warning: /home/oOoDJF/prog:2:
	Singleton variables: [X]
ERROR: '$runtoplevel'/0: Undefined procedure: program/0
   Exception: (3) program ? EOF: exit
https://ideone.com/HSpo4r
language:
Prolog (swi 7.6.4)
created:
9 years ago
visibility:
public

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