Florida State University: Dr. Penelope Kirby's "Property of Functions"
Please read the paper, paying special attention to examples 2.2.5, 2.2.6, and two functions 
and 
in the paragraph above example 2.7.1.
Click http://www.math.fsu.edu/~pkirby/mad2104/SlideShow/s4_2.pdf link to open resource.