In: Advanced Math
construct a bijective function of f:[0, inf) -> R
We are going to define a bijective function 
 from 
to 
. At
first we define 
. Then we
define the function interval-wise.
 for all
and  
.
Observe that image of (0,1] under f is (0,1] and image of (1,2] is
[-1,0). Similarly, we define 
, and 
. Again observe that image of (2,3] is (1,2] and image of (3,4] is
[-2,-1).
Again we define 
 and 
. Then the images will be (2,3] and [-3,-2) respectively. In
general, we define
and 
. Now it can be easily checked that 
 is a bijection. Infact, injectivity of this function is trivial
and for the surjectivity, let 
.
If 
, then 
.
If y>0, then 
 for some 
. Then 
. If y<0, then 
 for some n. Then 
. Hence 
 is
surjective.