A philosopher based in Leiden in The Netherlands. Research interests: Philosophy of Logic, Mathematics, and Language: exploring the possibilities of Mathematical Constructivism (especially in the form of Martin-Löf’s Constructive Type Theory) outside mathematics. Modern History of Logic: one focus is on Bolzano, Frege, and Wittgenstein’s Tractatus; another field of interest is the Metalogical Turn - Logic as Language versus Logic as Calculus.