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Three of the six DATC deviations were bugs

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The illegal/invalid line (6.A.5, 6.D.8). The document separates an order
that is impossible in this position from one this position allows that
merely did not come off. The first is ignored and its unit is holding like
any other; the second means the unit tried to leave and cannot be propped up
where it stands. An army sent across water with a fleet on the route and no
convoy ordered is the second; the identical order with nobody in the sea at
all is the first. Guessing at this once cost four passing cases to buy one.
Reading the document cost nothing -- it says so outright, in the note under
6.D.8 and again under 6.D.32.

A support that only looked like a hold (6.A.5). "Supports A Yorkshire" and
"Supports A Yorkshire - Yorkshire" are the same shape once parsed, and the
case turns on the difference: the first holds a unit down, the second
supports a move nobody can legally make. The extractor was throwing that
away; it now keeps it, and the fixture is regenerated.

The head of a cycle (6.F.22). Kruijswijk's resolver guesses that an order
fails, sees what follows, then guesses the other way. Only the outermost
order in a cycle may do that, because its answer is the one everything else
was computed against. This engine let any order that reached the dependency
list first declare the cycle its own -- and an inner one takes both guesses
with its callers' provisional answers held fixed, gets the same result twice
for that reason, and writes it down as settled. The cycle then becomes
invisible: the backup rule never runs and Szykman's rule never fires, and
the position resolves to whichever of its two consistent readings the search
happened to walk into first. It had been doing this on every paradox and
getting away with it, because on a first-order paradox both readings agree.

Also carried across from the reference algorithm: an order that resolved
itself while a nested call was away must not have the guess written over it.

Three remain. 6.F.28 and 6.F.29 are sixth-order paradoxes -- the same
twenty-six orders with one support between them, and the point of the pair
is that the answer swings on it, where this resolver gives both the same
answer. 6.G.19 the document itself gives three answers to, calls a little
bit pedantic, and advises adjudicators not to offer at all.
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@@ -107,7 +107,7 @@ published cases is parsed and run.
| Section | | Passing |
| --- | --- | --- |
| 6.A - 6.G | movement | 133 / 139 |
| 6.A - 6.G | movement | 136 / 139 |
| 6.H | retreating | 18 / 18 |
| 6.I | building | 7 / 7 |
| 6.J | civil disorder | 13 / 13 |
@@ -121,14 +121,45 @@ Three cases are excluded rather than failed. 6.A.6, 6.B.10 and 6.B.11 state
their setup in prose -- "Germany has a fleet in London" -- and the fixture is
built from order lines, so it cannot carry a unit nobody ordered.
Six are known deviations, written down so they are not rediscovered as
Three are known deviations, written down so they are not rediscovered as
surprises:
| Case | What it is |
| --- | --- |
| 6.A.5, 6.D.8 | The document distinguishes an `invalid` order from an `illegal` one, and the two cases disagree about whether a unit whose move was refused keeps its hold support. Guessing at the distinction cost four passing cases to buy one, so it is left until it can be read properly. |
| 6.F.22, 6.F.28, 6.F.29 | Second and sixth order paradoxes. The resolver settles them by Szykman's rule and reaches a different answer than the document's. These are positions nobody assembles by accident. |
| 6.G.19 | Whether an unnecessary fleet in a convoy chain signals intent. The document notes this one depends on which edition of the rules is used. |
| 6.F.28, 6.F.29 | Sixth order paradoxes: the same twenty-six orders with one extra support between them, which the document uses to show that the answer swings on it. The resolver gets five of the six sub-paradoxes right in both and the sixth wrong, and gives the same answer to both positions when the point is that they differ. These are positions nobody assembles by accident. |
| 6.G.19 | Whether an unnecessary fleet in a convoy chain signals intent. The document gives three different answers by edition, calls the question "a little bit pedantic", and advises that web adjudicators should not offer the order at all -- which is the line this one takes. |
### What the failing cases were worth
They found three real faults, which is the whole argument for running
somebody else's tests rather than only your own.
**The illegal/invalid line (6.A.5, 6.D.8).** The document separates an order
that is impossible *in this position* from one this position allows that
merely did not come off. The first is ignored and the unit is holding like
any other; the second means the unit tried to leave and cannot be propped up
where it stands. An army sent across water with a fleet on the route and no
convoy ordered is the second (6.D.8); the identical order with nobody in the
sea at all is the first (6.D.32). Guessing at this once cost four passing
cases to buy one. Reading it properly cost nothing.
**A support that only looked like a hold (6.A.5).** "Supports A Yorkshire"
and "Supports A Yorkshire - Yorkshire" are the same shape once parsed, and
the case turns on the difference: the first holds a unit down, the second
supports a move nobody can legally make. The extractor now keeps the
distinction; it was losing it.
**The head of a cycle (6.F.22).** Kruijswijk's resolver guesses that an order
fails, sees what follows, and guesses the other way. Only the *outermost*
order in a cycle may do that, because its answer is the one everything else
was computed against. This engine let any order that reached the dependency
list first declare the cycle its own -- and an inner one takes both guesses
with its callers' provisional answers held fixed, gets the same result twice
for that reason, and records it as settled. The cycle then becomes
invisible: the backup rule never runs, and the position resolves to
whichever of its two consistent readings the search walked into first. It
had been doing that on every paradox and getting away with it, because on a
first-order paradox both readings agree.
Sections H, I and J -- retreating and the winter -- have engine code but no
harness yet; their cases are shaped differently and need one.