I could not understand Lectures on Partial Differential Equations pass the first chapter, even if I have taken a course in pure math PDE (proving that convolving with the heat kernel is actually convergent, mean value property, maximum principle, etc), and another two courses in Lagrangian and Hamiltonian physics.
Arnold's verdict that it's good for undergrad students seems too optimistic. I think one reason for its difficulty is that it has too little explicit calculation and examples. Many statements are like implicit exercises I can't solve.
So what are prerequisites for studying V. Arnold's PDE? Maybe there is a set of lecture notes that expand on this textbook to make it readable, and supply with exercises and solutions?