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of nested s is . The culprit is the order in which iteration is executed: . The first disappears only after the whole sequence is unfolded.
*The computation according to the rules {b1 - b5, b7, r8 - r10} is more efficient in that respect. The iteration simulates the repeated loop over a block of code. The nesting is limited to , one recursion level per iterated function. showed this correspondence.
*These considerations concern the recursion depth only. Either way of iterating leads to the same number of reduction steps, involving

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