The set of even numbers less than 6 The set of even numbers less than 6 is ?
E = {$0, 2 ,4$}
Or
E= {...., $-2 , 0 , 2 ,4$ } 
Which answer is correct?
The definition of the even number is any number can be written as $x = 2n$. 
Is $$n \in \mathbb Z$$
or
$$n\in \mathbb N ? $$ 

The even integers less than $6$ are $\ldots, -2, 0, 2, 4$.
The even whole numbers less than $6$ are $0,2,4$.
The even natural numbers less than $6$ are either $0,2,4$ or perhaps only $2,4$.
"Even number" is even more ambiguous than "even natural number".
