FCMakeSymbols[name, range, type] generates a list or a sequence of symbols (depending on the value of type) by attaching elements of the list range to name.
For example, FCMakeSymbols[mu, Range[1, 3], List] returns {mu1,mu2,mu3}.
FCMakeSymbols[a, Range[1, 4], List]\{\text{a1},\text{a2},\text{a3},\text{a4}\}
f[FCMakeSymbols[a, Range[1, 4], Sequence]]f(\text{a1},\text{a2},\text{a3},\text{a4})
f[FCMakeSymbols[a, {1, 3}, Sequence]]f(\text{a1},\text{a3})