SPD[a, b] denotes a D-dimensional scalar product.
SPD[a, b] is transformed into
ScalarProduct[a, b,Dimension->D] by
FeynCalcInternal.
SPD[p] is the same as SPD[p,p] (=p^2).
Overview, PD, Calc, ExpandScalarProduct, ScalarProduct.
SPD[p, q] + SPD[q]p\cdot q+q^2
SPD[p - q, q + 2 p](p-q)\cdot (2 p+q)
Calc[ SPD[p - q, q + 2 p] ]-p\cdot q+2 p^2-q^2
ExpandScalarProduct[SPD[p - q]]-2 (p\cdot q)+p^2+q^2
SPD[a, b] // StandardForm
(*SPD[a, b]*)SPD[a, b] // FCI // StandardForm
(*Pair[Momentum[a, D], Momentum[b, D]]*)SPD[a, b] // FCI // FCE // StandardForm
(*SPD[a, b]*)FCE[ChangeDimension[SP[p, q], D]] // StandardForm
(*SPD[p, q]*)