Where formula _ 14 is the Levi-Civita symbol ( or permutation symbol ) and the last two forms for formula _ 15 are symmetric because formula _ 7 is equivalent ( formula _ 17 ) .
Where formula _ 14 is the Levi-Civita symbol ( or permutation symbol ) and the last two forms for formula _ 15 are equivalent because formula _ 7 is symmetric ( formula _ 17 ) .