Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

I would like just to check if my function which sends the positive integers numbers to the odd natural numbers and the non positive integers numbers to the even natural numbers is a bijection, more explicitly: $f:\mathbb Z\to \mathbb N, x\mapsto 2x-1$, if $x\gt0$ and $x\mapsto -2x$, if $x\le0$

I'm almost sure I'm right, it's just to be sure.


share|improve this question
It's correct. You need to prove it is bijective, though. –  egreg May 14 at 22:52
@egreg thanks for helping me :) –  user75086 May 14 at 22:58

1 Answer 1

up vote 2 down vote accepted

Yes it is.
Write up its inverse.

share|improve this answer
Thanks for your help :) –  user75086 May 14 at 22:59

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.