• the line at time t = i
• the tab at time t = j
• statement at line i, tab j = for target in iterable_ex:
• value at j in map (Control Map at time t) = trio ("for", i, [ elem, rest ])

then Control Map at time (t + 1) = result of storing (trio ("for", i, rest)) at key: j in map: (Control Map at time t)