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I don't understand what the last paragraph of the attached page means. Why does the Kronecker delta being an invariant symbol mean that the product of a representation R and its complex conjugate representation has the singlet representation with all matrices being zero?
Doesn't the number zero always form a trivial onedimensional representation of any group, because when plugged into the equation ##[T ^a , T ^b] = i f^{\text{abc}} T^c## it trivially satisfies it?
Doesn't the number zero always form a trivial onedimensional representation of any group, because when plugged into the equation ##[T ^a , T ^b] = i f^{\text{abc}} T^c## it trivially satisfies it?
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