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