Elements Of Partial Differential Equations By Ian Sneddon.pdf -

Looking at the chapters, probably starts with definitions, first-order equations, wave and heat equations, Laplace's equation. Then methods like separation of variables, Fourier series, Green's functions. Maybe some special functions like Bessel functions. It's important to mention the mathematical rigor versus intuitive approach. Since Sneddon is a mathematician, there might be proofs, which could be a plus for a theory-focused reader but maybe a bit dense for someone looking for applied methods.