FCDisableTraditionalFormOutput[] sets the output format
of the current FrontEnd to StandardForm. The setting is not
persistent, such that it does not influence any subsequent Mathematica
FrontEnd sessions.
Overview, $FCTraditionalFormOutput, FCDisableTraditionalFormOutput.
FCDisableTraditionalFormOutput[]
FV[p, \[Mu]]\overline{p}^{\mu }
FCEnableTraditionalFormOutput[]
FV[p, \[Mu]]\overline{p}^{\mu }