Complex sentence: Lanczos' Ph.D. thesis (1921) was on relativity theory, he sent his thesis copy to Einstein and Einstein wrote back saying I have read your work in as much detail as my present excess of work allows.
Split into simpler sentences: Lanczos' Ph.D. thesis (1921) was on relativity theory. He sent his thesis copy to Einstein, and Einstein wrote back, saying: I have read your work in as much detail as my present excess of work allows.