A friend of mine told me that (by his teacher) 0 is an even and positive number, how can it be?
0 is definitely an even number, since it may be written as 2*n, where n is some integer.
I think it's more usual to say that 0 is a non-negative number, but I'm not sure..
0 is definitely not a positive number. Positive means greater than zero, and zero is certainly not greater than itself.
for as far as I know, 0 is both positive and negative.
I suppose I will hear no argument if I say that 0 is in both N+ and N-, so that pretty much solves it, no?
All the definitions of positive numbers that I've ever seen exclude zero. So zero is not a positive number. However it is true that it is an even number.
Both or Neither
Depending on the situation, zero may be considered to be positive, negative, both, or neither.
In some computers, negative and positive zero may be different, but in normal mathematics, whether zero is considered to be positive depends somewhat on context.
By standard logic there is the excluded middle rule.
Is there any influence based on this rule and the definition of 0 (positive, negative, both, or neither)?
It is a matter of convention. To avoid confusion one should say things like strictly positve and so on. It is no different from saying greater rthan and not specifiying if we mean strictly or posisibly equal. It shuold be no great hardship to make oneself clear.
Is there any formal and rigorous way to show the difference between 'strictly positive' and 'positive'?
What is 'posisibly equal'?
"What is 'posisibly equal'?"
A typo. It should read possibly.
I wouldn't consider computer practice to say anything at all about mathematics!
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