Develop a simple set of rules for diagnosing respiratory symptom diseases given patient symptoms, using the following knowledge of typical symptoms. Describe how a simple backward chaining interpreter could be used to go through the possible diagnoses, asking the user questions about their symptoms. If you have an expert system shell available, try implementing a simple diagnosis system based on the above.

Influenza: Symptoms include a persistent dry cough and a feeling of general malaise.

Hayfever: Symptoms include a runny nose and sneezing. The patient will show a positive reaction to allergens, such as dust or pollen.

Laryngitis: Symptoms include a fever, a dry cough, and a feeling of general malaise. A "laryngoscopy" will reveal that the person has an inflamed larynx.

Asthma: Symptoms include breathlessness and wheezing. If it is triggered by an allergen, such as dust or pollen, it is likely to be "extrinsic asthma". "Intrinsic asthma" tends to be triggered by exercise, smoke or a respiratory infection.