FeynCalcInternal[exp] translates exp into
the internal FeynCalc (abstract data-type) representation.
Overview, FeynCalcExternal, FCI, FCE.
ex = {GA[\[Mu]], GAD[\[Rho]], GS[p], SP[p, q], MT[\[Alpha], \[Beta]], FV[p, \[Mu]]}\left\{\bar{\gamma }^{\mu },\gamma ^{\rho },\bar{\gamma }\cdot \overline{p},\overline{p}\cdot \overline{q},\bar{g}^{\alpha \beta },\overline{p}^{\mu }\right\}
ex // StandardForm
(*{GA[\[Mu]], GAD[\[Rho]], GS[p], SP[p, q], MT[\[Alpha], \[Beta]], FV[p, \[Mu]]}*)ex // FeynCalcInternal\left\{\bar{\gamma }^{\mu },\gamma ^{\rho },\bar{\gamma }\cdot \overline{p},\overline{p}\cdot \overline{q},\bar{g}^{\alpha \beta },\overline{p}^{\mu }\right\}
ex // StandardForm
(*{GA[\[Mu]], GAD[\[Rho]], GS[p], SP[p, q], MT[\[Alpha], \[Beta]], FV[p, \[Mu]]}*)FeynCalcExternal[ex] // StandardForm
(*{GA[\[Mu]], GAD[\[Rho]], GS[p], SP[p, q], MT[\[Alpha], \[Beta]], FV[p, \[Mu]]}*)ex = FCI[{SD[a, b], SUND[a, b, c], SUNF[a, b, c], FAD[q], LC[\[Mu], \[Nu], \[Rho], \[Sigma]]}]\left\{\delta ^{ab},d^{abc},f^{abc},\frac{1}{q^2},\bar{\epsilon }^{\mu \nu \rho \sigma }\right\}
ex // StandardForm
(*{SUNDelta[SUNIndex[a], SUNIndex[b]], SUND[SUNIndex[a], SUNIndex[b], SUNIndex[c]], SUNF[SUNIndex[a], SUNIndex[b], SUNIndex[c]], FeynAmpDenominator[PropagatorDenominator[Momentum[q, D], 0]], Eps[LorentzIndex[\[Mu]], LorentzIndex[\[Nu]], LorentzIndex[\[Rho]], LorentzIndex[\[Sigma]]]}*)