Herbert Federer is a foundational figure in , having authored the field's definitive textbook and several seminal papers. Depending on your level of expertise, here are the most important works to look for in PDF format: 1. The Definitive Textbook Geometric Measure Theory

Federer writes in an extraordinarily precise, almost formalist style. Lemma 1.2 might reference a result from Appendix 2.3.1, which uses notation defined in Chapter 0, §4. You will flip pages (or scroll frantically) constantly. This is not a beach read.

This contains the and the differentiation of measures —tools essential for proving the area formula.