I wish I could understand even 5% of this paper. Even in 3 lines of code, there are so, so, so many implications of what could happen… How do fellow lobste.rs deal with “semantic-heavy” code like this?
Reading PL research papers does typically require some background knowledge. In this case, the paper assumes some knowledge of how type systems are specified. A good place to start learning this might be the Types and Programming Languages textbook by Benjamin Pierce .