```
PROLOG: “Syntax error: Operator expected”
ERROR: c:/users/zulfekarali/Desktop/KBS/kbs.pl:2:3: Syntax error: Operator expected
% c:/Users/ZulfekarAli/Desktop/KBS/kbs.pl compiled 0.00 sec, 27 clauses

--------

domains
    disease,indication = symbol
    Patient,name = string

predicates
    hypothesis(string,disease)
    symptom(name,indication)
    response(char)
    go
clauses
    go :-
        write("What is the patient's name? "),
        readln(Patient),
        hypothesis(Patient,Disease),
        write(Patient,"probably has ",Disease,"."),nl.

    go :-
        write("Sorry, I don't seem to be able to"),nl,
        write("diagnose the disease."),nl.

    symptom(Patient,fever) :-
        write("Does ",Patient," have a fever (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,rash) :-
        write("Does ",Patient," have a rash (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,headache) :-
        write("Does ",Patient," have a headache (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,runny_nose) :-
        write("Does ",Patient," have a runny_nose (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,conjunctivitis) :-
        write("Does ",Patient," have a conjunctivitis (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,cough) :-
        write("Does ",Patient," have a cough (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,body_ache) :-
        write("Does ",Patient," have a body_ache (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,chills) :-
        write("Does ",Patient," have a chills (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,sore_throat) :-
        write("Does ",Patient," have a sore_throat (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,sneezing) :-
        write("Does ",Patient," have a sneezing (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,swollen_glands) :-
        write("Does ",Patient," have a swollen_glands (y/n) ?"),
        response(Reply),
        Reply='y'.

    hypothesis(Patient,measles) :-
        symptom(Patient,fever),
        symptom(Patient,cough),
        symptom(Patient,conjunctivitis),
        symptom(Patient,runny_nose),
        symptom(Patient,rash).

    hypothesis(Patient,german_measles) :-
        symptom(Patient,fever),
        symptom(Patient,headache),
        symptom(Patient,runny_nose),
        symptom(Patient,rash).

    hypothesis(Patient,flu) :-
        symptom(Patient,fever),
        symptom(Patient,headache),
        symptom(Patient,body_ache),
        symptom(Patient,conjunctivitis),
        symptom(Patient,chills),
        symptom(Patient,sore_throat),
        symptom(Patient,runny_nose),
        symptom(Patient,cough).    

    hypothesis(Patient,common_cold) :-
        symptom(Patient,headache),
        symptom(Patient,sneezing),
        symptom(Patient,sore_throat),
        symptom(Patient,runny_nose),
        symptom(Patient,chills).

    hypothesis(Patient,mumps) :-
        symptom(Patient,fever),
        symptom(Patient,swollen_glands).

    hypothesis(Patient,chicken_pox) :-
        symptom(Patient,fever),
        symptom(Patient,chills),
        symptom(Patient,body_ache),
        symptom(Patient,rash).

    hypothesis(Patient,measles) :-
        symptom(Patient,cough),
        symptom(Patient,sneezing),
        symptom(Patient,runny_nose).

    response(Reply) :-
        readchar(Reply),
        write(Reply),nl.

```