During the summer, I plan on learning differential equations (ODE's and PDE's) from bottom to top, but I am unable to choose books due to a great variety present. Can you suggest books for me to read in the following order (you can add as many books in each section if you like); Ordinary Differential Equations (Introduction) 1. ? (Undergraduate) 1. ? 2. ? 3. ? (Graduate) 1. ? 2. ? and the same format for partial differential equations. I would really appreciate it.