The front deepens down a rung
Worth reading first: The organ that was taken away · Counting the spirals · A head is a set of points.
A removal is felt at all only within the front — the run of most recent organs whose placement was set against the one now missing — and this collection has measured that depth and found it to be the larger of the two counted numbers. Past it, nothing wrecks: cuts made sixteen organs back on a stem whose front is thirteen deep repair without exception.
That is a statement about one stem. Swept along a rung it becomes a statement about a range of stems that a counter cannot tell apart, and then it does some work.
The front is worth holding onto as a physical object rather than a number. It is not a window chosen for convenience: it is the set of organs whose azimuths were set while the removed organ was part of the neighbourhood being minimised over, and it ends where that influence falls below what the arrangement can register. A disturbance that arrives after the rule has chosen moves nothing at all, which is the same fact from the other side.
One to five, with the pair held
Twelve rises from 0.018 to 0.007. Every one of them is counted at 5 and 8 spirals. The number of offsets that never repair runs from one to five.
At the coarse end a single offset wrecks. By the middle of the rung there are two. Past 0.011 there are four or five, and the ones that have appeared are the deeper offsets — six, seven, eight — which simply did not exist as possibilities at the top of the rung because a removal that far back was not felt.
It is worth being careful about what “did not exist” means, because it is not that those cuts were never made. Every offset out to two organs past the front is cut at every rise; the deep ones at the coarse end simply repair. A cut that heals is not a missing measurement, it is a measurement whose answer is no wreck, and the growth in the count is the growth in how many cuts answer otherwise. The census that established this reports the healed offsets for exactly that reason: a table showing only the cuts with an answer would be a picture of the selection rather than of the sweep.
Which is most of the story, and not all of it
The deepening explains the count without any new mechanism. A front three organs deep offers three places to cut; a front eight deep offers eight. If the rule for which family survives were fixed and correct, the number of wrecked offsets would still grow down a rung.
What it does not explain is which family the new offsets keep, and that is where the arithmetic and the mechanism meet. The offsets that appear at the fine end are the ones beyond the smaller counted number, and the offset rule says those keep the larger family. They do.
So the rule’s two clauses are not two halves of one statement. The first clause applies at every rise of the rung, because the shallow offsets exist at every rise. The second clause has nothing to apply to until the front is deep enough to have offsets past the smaller number — which happens partway down the rung and not at the top of it.
That asymmetry is invisible in the census the rule was scored on and it changes what the score means. Twenty-five of thirty reads as a rule that is mostly right; read along a rung it is closer to two rules with different domains, one of which has been tested everywhere and one of which has been tested wherever the sampling happened to land. Neither is refuted here. What is refuted is the idea that the thirty rows were thirty comparable tests of one statement.
What that does to a score
A rule scored over a census assembled from one rise per rung is being scored on a sample that never varies the thing its second clause depends on. Twenty-five of thirty is a real number and it is not a number about the rule; it is a number about the census.
The rule is not the only published number this sweep unsettles. The depth of the front was itself measured one rise at a time, and it slides too.
The measurement that established it reports that the front runs as deep as the larger of the two counted numbers — thirteen organs on an 8/13 stem, eight on a 5/8 one — and that past it nothing wrecks. On this rung the larger counted number is eight, and it is a constant: a counter returns 5 and 8 at every rise from 0.018 down to 0.007. The depth does not follow it. At the coarse end a single offset never repairs; by 0.012 there are two; only from 0.011 down do offsets as far back as eight wreck at all.
So the front is as deep as the larger counted number is true at the fine end of this rung and false across most of its width, and the procedure that established it could not have shown that. It is the same failure the rest of this essay is about, one step further back, and it is worth naming in those terms rather than filing as a separate correction: a quantity was measured on stems chosen for their counted pairs, came out equal to a number a counter reports, and was written down as though the equality were a law. What it is instead is the value that quantity takes at the rises the census happened to sample.
The honest form of the statement is a bound rather than an equation. The larger counted number is the deepest the front reaches anywhere on a rung, reached near the fine end and not before; elsewhere it is shallower, by a factor of eight at the coarse end of this one. A bound is the weaker claim and it survives the sweep, which is the trade this collection keeps making — and it is also the claim that would have predicted the anomaly rather than been surprised by it.
Concretely: at the coarse end of this rung the second clause is untestable, because no offset past five ever wrecks. Any census that happened to sample 0.018 rather than 0.010 would have found a rule with one clause and no evidence about the other, and would have reported it as a rule that works.
The lattices in the census were not chosen to make this happen, which is why it is worth reporting rather than apologising for. They were chosen to span two branches and a range of pairs — the right criteria for the question which pair — and the rise attached to each was whatever rise produced that pair. Nothing about that procedure is careless. It simply optimises for a different question from the one the rule ended up making a claim about, and the gap between those two questions is where the incompleteness lived.
The general form is worth stating because this collection will meet it again. A sample assembled to vary one quantity holds others fixed by construction, and any rule later fitted to that sample inherits the constancy as an untested assumption. The fix is not a better sample; it is noticing which quantity the rule turned out to depend on, and going back to vary that one on purpose.
The depth is not the whole of the rung either
Two things move along a rung, and the deepening is only one of them. The two contact steps also change places, and the two changes do not happen at the same rise: the steps cross at 0.015 and the deep offsets appear at 0.011.
That the two are separated by four rises is useful, because it means the sweep can tell them apart in principle. Whatever decides the survivor, it is not the step ordering alone — the ordering reverses at 0.015 and the answers do not change there.
This is the one place in the thread where two candidate explanations have been put on the same axis and separated by measurement rather than by argument. The step ordering was the natural candidate, because the reading it refutes is stated in exactly those terms; and it fails, because a quantity that reverses four rises above the only change in the answers is not the quantity the answers are following. What is left is the depth, which does line up — and a depth that decides an answer is a mechanism rather than a coincidence of arithmetic.
Three controls
The front is measured, not assumed. The depth used here is the count of offsets that actually fail to repair, read off the cuts themselves, rather than the larger counted number quoted as a proxy for it. The two agree at the rises where both are available, which is the check worth having.
Nothing here depends on the resolution. A thousandth puts twelve rises inside this rung. Halving the step would double the samples and produce the same monotone growth, because what is being resolved is a slide rather than a feature with a width.
And the growth is not an artefact of the settling test. Every rise on the rung settles by the same criterion every other run on this site uses, and a stem that failed it would be excluded rather than counted as a wreck. That distinction matters here more than usual: a stem that never settles in the first place and a stem that settles and is then wrecked by a cut look similar in the divergence trace and are entirely different objects, and only the second is what this sweep counts. The coarse ladder has rises of the first kind — a band that sticks on a rational — and they are excluded from every ablation table on this site for exactly this reason.
What it predicts
If the deepening is what governs how many offsets are available, then a finer rung — with larger counted numbers and a deeper front — should offer more of them, and the count should grow the same way inside it.
The cost of that test is worth stating, because it is the reason it has not been run. Each rise on a rung is a settled stem plus one cut stem per offset, each grown to settle again and compared against a control sharing its history; a finer rung has more offsets and needs longer stems to settle at all, so the work grows faster than the rung count does. That is an argument for doing it once and banking the numbers, not an argument against doing it.
That is a cheap test and it is the obvious next sweep. It also matters for the reading about which family lost a member, which can only be asked at offsets that are multiples of a counted number: a deeper front at 8/13 has both 8 and 13 available where a 5/8 front has 5 and 8, so the same sweep would widen the rows that reading is scored on.
Where this leaves it
The picture that comes out of this is less tidy than a rule and more useful. There is no single quantity that decides which family a wrecked stem keeps. There is a front whose depth is set by the rise, a set of offsets that exist because of that depth, and a rule over those offsets that has been scored without ever varying the depth.
A count is a robust description and its robustness is its blindness: it is the same number over a range of geometries. That is what makes it worth measuring on a plant, and it is why an account of ablation stated only in counted numbers has been quietly incomplete for as long as this thread has been running.
There is a version of this essay that overstates it, and it is worth naming so that this one does not become it. The claim here is not that the counted pair is uninformative about ablation: it fixes which two families are available at all, and that restriction is the strongest result the thread has. The claim is narrower — that the pair does not fix which of the two survives, because the quantity that does is one the pair holds constant over. A description can be exactly right about what it describes and silent about the question being asked of it, and telling those two apart is most of what measuring anything is for.
What links here
Computed from the collection, not written here: the essays that point at this one.
Shares its objects with
Essays that name at least two of the same things, and that neither author linked.
- The organ that was nobody's neighbour — both name ablation, claim testing, control, honest limits, lattice, lattice offset, measurement, negative result, parastichy pair, the placement rule, rigid hop, rung
- A stem too fine to settle — both name claim testing, control, honest limits, lattice, measurement, negative result, parastichy pair, the placement rule, rise, rung
- The band was not the sampling — both name claim testing, control, honest limits, lattice, measurement, negative result, parastichy pair, the placement rule, rise, rung
- The hop that survived — both name ablation, honest limits, lattice, lattice offset, measurement, parastichy pair, the placement rule, rigid hop, rise, rung
- Two accounts of one number — both name ablation, claim testing, honest limits, lattice, measurement, negative result, parastichy pair, the placement rule, rise, rung
- One turn per survivor — both name ablation, honest limits, lattice, lattice offset, measurement, parastichy pair, the placement rule, rigid hop, rise
Named objects
A flat tag is an object no other essay names yet.
AblationClaim testingControlHonest limitsLatticeLattice offsetMeasurementNegative resultNodes per rungParastichy pairThe placement ruleRigid hopRiseRung