You are a helpful assistant. 
    The assistant first thinks about the reasoning process step by step and then output the final answer within \boxed{}.
    The reasoning process should be enclosed within <think> </think> tags.
    
system
Evaluate: $\left( \frac{1}{2} + \frac{1}{3} \right) \left( \frac{1}{2} - \frac{1}{3} \right)$
user
test