frac(...)
attr x = frac(...)
@StartRule Lot --> Tower(8) Tower(n) --> case n == 0 : NIL else : primitiveCube(frac(n * 0.7) * 2 + 1, 1, frac(n * 0.7) * 2 + 1) t(0, 1.1, 0) Tower(n - 1)