You can load (and are expected to if you intend to use them) an arbitrary number of iteration variable from the iterated table (or the common table shared if you load from different tables) e.g

table T = extend.range(5)
table U[u] = by T.N mod 2
T.N2 = T.N + 2
T.N3 = T.N + 3

T.S = for tn in T.N, tn2 in T.N2, tn3 in T.N3, un in u
  ...
  return ...