Operator mixing in N=4 SYM can be regarded as the permutation of indices. We introduce the permutation group to label all possible gauge-invariant operators, and interpret the correlation functions as geometric objects of topological theory. In addition, permutations can be Fourier transformed to irreducible representations of finite groups, which allows us to solve finite N constraints. \\ \\ This talk is based on the collaboration with Yusuke Kimura (Okayama) and Sanjaye Ramgoolam (Queen Mary).