GSLR[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. 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, GALP, GALN, GALR, GSLP, GSLN.
GSLR[p, n, nb]\bar{\gamma }\cdot \overline{p}_{\perp }
StandardForm[GSLR[p, n, nb] // FCI]
(*DiracGamma[LightConePerpendicularComponent[Momentum[p], Momentum[n], Momentum[nb]]]*)Notice that the properties of n and nb vectors have to be set by hand before doing the actual computation
GSLR[p, n, nb] . GSLP[q, n, nb] // DiracSimplify-\frac{1}{4} \overline{n}^2 \left(\overline{\text{nb}}\cdot \overline{q}\right) \left(\bar{\gamma }\cdot \overline{\text{nb}}\right).\left(\bar{\gamma }\cdot \overline{p}_{\perp }\right)-\frac{1}{4} \left(\overline{n}\cdot \overline{\text{nb}}\right) \left(\overline{\text{nb}}\cdot \overline{q}\right) \left(\bar{\gamma }\cdot \overline{n}\right).\left(\bar{\gamma }\cdot \overline{p}_{\perp }\right)
FCClearScalarProducts[]
SP[n] = 0;
SP[nb] = 0;
SP[n, nb] = 2;GSLR[p, n, nb] . GSLP[q, n, nb] // DiracSimplify-\frac{1}{2} \left(\overline{\text{nb}}\cdot \overline{q}\right) \left(\bar{\gamma }\cdot \overline{n}\right).\left(\bar{\gamma }\cdot \overline{p}_{\perp }\right)
FCClearScalarProducts[]