Per Martin-Löf

Per Martin-Löf, a Swedish logician, developed a predicative type theory. This theory aimed to provide a foundation for mathematics that avoided impredicative constructions, which involve self-referencing definitions. While classical analysis often relies on such constructions, Martin-Löf's theory sought to establish a more rigorous, predicative approach. However, it is not universally considered adequate for all of classical analysis.1

Logic, as a discipline, has evolved significantly, with modern logic emerging after the Renaissance. Early developments in the 20th century, building on the work of logicians like Frege and Peano, focused on using symbolic techniques. This led to the concept of formal systems, characterized by axioms and rules of inference, aiming to derive theorems. Proof theory, a branch of logic, studies these formal aspects and the nature of proofs within these systems.2