Abstract

Recent years have witnessed an explosion of studies of the non-invertible symmetries in various dimensions. In this talk, I will revisit the most vanilla type of non-invertible symmetry — Kramers-Wannier duality symmetry in (1+1)d, from three different perspectives: 1. lattice; 2. field theory; 3. Symmetry TFT. I will explain the construction of non-invertible defects, their fusion rules, and F-symbols.