How many functions are both even and odd?  (Assume that the domain of the function is the set of all real numbers.)
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
How many functions are both even and odd?  (Assume that the domain of the function is the set of all real numbers.)
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
1
How many functions are both even and odd?  (Assume that the domain of the function is the set of all real numbers.)
train