FVLR[p,mu,n,nb] denotes the perpendicular component in the lightcone decomposition of the Lorentz vector p^{\mu } along the vectors n and nb. It corresponds to p^{\mu }_{\perp}.
If one omits n and nb, the program will use default vectors specified via $FCDefaultLightconeVectorN and $FCDefaultLightconeVectorNB.
Overview, Pair, FVLN, FVLP, SPLP, SPLN, SPLR, MTLP, MTLN, MTLR.
FVLR[p, \[Mu], n, nb]\overline{p}^{\mu }{}_{\perp }
FVLR[p, \[Mu], n, nb] // FCI // StandardForm
(*Pair[LightConePerpendicularComponent[LorentzIndex[\[Mu]], Momentum[n],Momentum[nb]], LightConePerpendicularComponent[Momentum[p], Momentum[n], Momentum[nb]]]*)FVLR[p, \[Mu], n, nb] FVLR[q, \[Mu], n, nb] // Contract\overline{p}\cdot \overline{q}_{\perp }
FVLR[p, \[Mu], n, nb] . FVLP[q, \[Mu], n, nb] // Contract0