2-Group symmetries in class S

2-group symmetries are generalized that arise when 1-form and 0-form mix with each other. We uncover the existence of a class in general 4d N=2 theories Class S can be constructed by compactifying 6d N=(2,0) SCFTs on Riemann surfaces carrying arbitrary regular punctures outer-automorphism twist lines. The structure captured terms equivalence classes line defects plus flavor Wilson lines, which thought as accounting for screening while keeping track charges. describe method computing these theory using data Riemman surface used its parent theory.