One mistake students sometimes make is the so-called `proof by example'. The proof by example refers to the situation where the statement is validated for some examples or cases rather than validating for the general case. 

Consider the following claim and explanation. Is the explanation valid?

Claim:

"If is a prime number then is also a prime number."

Explanation:

"The statement holds for . Therefore, the statement is true for all prime numbers , that is, if is prime then is also prime."