GSLRD[p,n,nb] denotes the perpendicular component in the lightcone decomposition of the slashed Dirac matrix (\gamma \cdot p) along the vectors n and nb in D dimensions. It corresponds to (\gamma \cdot p)_{\perp}.
If one omits n and nb, the program will use default vectors specified via $FCDefaultLightconeVectorN and $FCDefaultLightconeVectorNB.
Overview, DiracGamma, GALPD, GALND, GALRD, GSLPD, GSLND.
GSLRD[p, n, nb]\gamma \cdot p_{\perp }
StandardForm[GSLRD[p, n, nb] // FCI]
(*DiracGamma[LightConePerpendicularComponent[Momentum[p, D], Momentum[n, D], Momentum[nb, D]], D]*)Notice that the properties of n and nb vectors have to be set by hand before doing the actual computation
GSLRD[p, n, nb] . GSLPD[q, n, nb] // DiracSimplify-\frac{1}{4} n^2 (\text{nb}\cdot q) (\gamma \cdot \;\text{nb}).\left(\gamma \cdot p_{\perp }\right)-\frac{1}{4} (n\cdot \;\text{nb}) (\text{nb}\cdot q) (\gamma \cdot n).\left(\gamma \cdot p_{\perp }\right)
FCClearScalarProducts[]
SPD[n] = 0;
SPD[nb] = 0;
SPD[n, nb] = 2;GSLRD[p, n, nb] . GSLPD[q, n, nb] // DiracSimplify-\frac{1}{2} (\text{nb}\cdot q) (\gamma \cdot n).\left(\gamma \cdot p_{\perp }\right)
FCClearScalarProducts[]