FVLRD[p,mu,n,nb] denotes the perpendicular component in the lightcone decomposition of the Lorentz vector p^{\mu } along the vectors n and nb in D dimensions. 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, FVLND, FVLPD, SPLPD, SPLND, SPLRD, MTLPD, MTLND, MTLRD.
FVLRD[p, \[Mu], n, nb]p^{\mu }{}_{\perp }
FVLRD[p, \[Mu], n, nb] // FCI // StandardForm
(*Pair[LightConePerpendicularComponent[LorentzIndex[\[Mu], D], Momentum[n, D], Momentum[nb, D]], LightConePerpendicularComponent[Momentum[p, D], Momentum[n, D], Momentum[nb, D]]]*)FVLRD[p, \[Mu], n, nb] FVLRD[q, \[Mu], n, nb] // Contractp\cdot q_{\perp }
FVLRD[p, \[Mu], n, nb] . FVLPD[q, \[Mu], n, nb] // Contract0