 Second, Dedekind’s contributions to algebraic number theory were connected, in a natural and fruitful way, with Evariste Galois’ revolutionary group-theoretic approach to algebra. In fact, Dedekind’s early and systematic study of Galois theory—he was  the first to lecture on it at a German university, already during his time as a Privatdozent in Göttingen—led  to a transformation of that theory itself. It turned from the study of substitutions in formulas and of functions invariant under such substitutions into the study of field extensions and corresponding automorphisms, which deep connections to algebraic number theory (Mehrtens 1979b, Stein 1988, Ferreirós &amp; Reck 2020).  Dedekind also introduced additional applications of Galois theory, e.g., in the study of modular equations and functions (Gray 2000, ch. 4, Alten et al. 2003, ch. 8).