I'm currently reading logic and have some issues with the contrapositve of this statement:

The textbook says:

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> If $n>0$ and $4n−1$ is prime, then $n$ is odd
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> 
> 

I understand the contrapositive thinking (I think!) $P\to Q$ becomes with this logic $\neg Q\to\neg P$

Therefore in my mind this statement should be:

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> If n is even, then $0>n$ and $4n-1$ is not prime.
> 
> 
> 

But this does not even make sense. Are there any rules I'm missing?