Imagine you were commissioned to develop a medical expert 
system to simulate the expertise of a doctor.   The facts 
will consist of few diseases and their corresponding symptoms.

Some example are:
/*   Medical Expert System     */
/*  cyberDOC(disease,symptom). */

cyberDOC(cold,sneezing).
cyberDOC(cold,headache).
cyberDOC(cold,runny_nose).
cyberDOC(flu,headache).
cyberDOC(flu,shivery).
cyberDOC(flu,temperature).
cyberDOC(brain_tumour,headache).

Feel free to add other creative facts.
		
Write queries to:
a) List all the diseases in the medical database
b) List the symptoms of flu
c) Find what could be causing a headache