'Prolog Procedure si(A) Does not Exist

This is the code

verificar(S) :-
    (si(S)
    ->  
    true ;
    (no(S)
    ->  
    fail ;
    preguntar(S))).

preguntar(Pregunta) :-
    write('Tiene los siguientes sintomas: '),
    write(Pregunta),
    write('?'),
    read(Respuesta),
    nl,
    ( (Respuesta == si)
    ->  
    assert(si(Pregunta));
    assert(no(Pregunta)), fail).

and the problem is

procedure `si(A)' does not exist
Reachable from:
      verificar(A)
      resfriado
      hipotesis(A)
      evaluar

prolog

Solution 1:^[1]

The problem is for the first run, the program does not know what you mean with si(A) since there is no predicate or rule defined. Quickfix: Add dummy data like

si(nothing).
no(nothing).

which can be removed after the first "valid" entry in your knowledge base.

Solution 2:^[2]

You have not written the predicate for si(). This is why you are getting the error:-

procedure `si(A)' does not exist

Sources

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Source: Stack Overflow

Solution	Source
Solution 1	DuDa
Solution 2	Reema Q Khan

'Prolog Procedure si(A) Does not Exist

Solution 1:[1]

Solution 2:[2]

Sources

Related Questions

Solution 1:^[1]

Solution 2:^[2]