I will be starting graduate school in statistics in August. I purchased The Statistical Sleuth recently [you can view the table of contents by clicking on the "Look Inside" link], and I do think it is a great book.
However, I am the type of person who likes to learn theory alongside applications, i.e., in a theorem-proof-example setting, and this textbook seems to only emphasize practical examples over theory. I would just like to be given a formula and be provided a proof that it is true.
Does there exist a textbook that combines both of these theoretical and practical aspects?
Code examples wouldn't be necessary, but would be a huge bonus.
ETA: One textbook that I personally really liked was Mathematical Statistics with Applications by Wackerly et al., but that is at an undergraduate level and does not cover as many methods as The Statistical Sleuth.