I have a few questions regarding the above mentioned task. One has to show whether or not these functions are injective, surjective or bijective.
This seems straightforward for most of these functions:
(1) Not injective since some values are hit multiple times. Also not surjective since not every y has a corresponding x.
(2) Bijective, since there is a one to one correspondance.
(3) Bijective, since it's only from the natural numbers, so every value will be hit exactly once
(4) Don't quite understand where to start with this one.
My question now is: How do I properly phrase this? Some of these seem quite intuitive but I'm struggling with the correct notation of this.