ExplicitSUNFIndex[ind]
is a specific SU(N) index in the fundamental representation, i.e. ind
is an integer.
Overview, SUNIndex, SUNFIndex.
[1] ExplicitSUNFIndex
1
[a, 1, 2] SUNTF
T_{12}^a
[a, 1, 2] // FCI // StandardForm
SUNTF
(*SUNTF[{SUNIndex[a]}, ExplicitSUNFIndex[1], ExplicitSUNFIndex[2]]*)