Vorlesungen
Some recommended textbooks:
Haim Brezis: Functional Analysis, Sobolev Spaces and Partial Differential Equations. https://link.springer.com/book/10.1007/978-0-387-70914-7
Jan van Neerven: Functional Analysis
https://www.cambridge.org/core/books/functional-analysis/62B852DFB4D6F11D21C04309DCF7584F
Philippe Ciarlet: Linear and nonlinear functional analysis with applications. Second edition.
https://epubs.siam.org/doi/10.1137/1.9781611978247