LeftRightNablaD2[mu] denotes \overleftrightarrow{\nabla }_{i}, acting to
the left and right.
ExplicitPartialD[LeftRightNablaD2[mu]] gives
(RightNablaD[i] + LeftNablaD[i]).
Overview, ExplicitPartialD, ExpandPartialD, FCPartialD, LeftNablaD, RightNablaD.
LeftRightNablaD2[i]
ExplicitPartialD[%]\overleftrightarrow{\nabla }_i
-\overleftarrow{\partial }_i-\vec{\partial }_i
LeftRightNablaD2[i] . QuantumField[A, LorentzIndex[\[Nu]]]
ExpandPartialD[%]\overleftrightarrow{\nabla }_i.A_{\nu }
-\left(\partial _iA_{\nu }\right)-\overleftarrow{\partial }_i.A_{\nu }
QuantumField[A, LorentzIndex[\[Mu]]] . LeftRightNablaD2[i] . QuantumField[A, LorentzIndex[\[Rho]]]
ExpandPartialD[%]A_{\mu }.\overleftrightarrow{\nabla }_i.A_{\rho }
-A_{\mu }.\left(\partial _iA_{\rho }\right)-\left(\partial _iA_{\mu }\right).A_{\rho }