[TimelordUK]

R13 slice 2, the one slice in the plan that changes answers. ArithmeticEvaluator, which serves SELECT, HAVING and join conditions, now evaluates predicates in three-valued logic, with NULL standing for UNKNOWN. Closes P48 and P50.

What changed

Arm	Before	Now
Comparisons	compare_with_op, no NULL guard: NULL vs value was false, NULL vs NULL was equal	predicate-layer compare_trilean: NULL on either side gives NULL
AND / OR / NOT	collapsed through to_bool (NULL → false)	Trilean truth tables; to_bool deleted
IN / NOT IN	two-valued; NULL matched NULL	OR's truth table; NOT IN is its negation
BETWEEN	two comparisons joined with &&	AND's truth table
LIKE	stringified NULL	NULL for a NULL operand
simple CASE x WHEN NULL	matched a NULL x	never matches

compare_values still reports NULL = NULL as equal. ORDER BY needs that, so the NULL test sits at the predicate layer, as R10 did for WHERE.

Trilean::from_value / to_value are now the single crossing between DataValue and the truth tables.

Acceptance, as slice 1 set it

• Evaluator matrix: all 32 value-evaluator KNOWN entries went FIXED in this one change, and the WHERE column did not move. The value evaluator went from 4/36 to 36/36, and KNOWN is now empty (the mechanism stays).
• Parity: moved by exactly the six P48/P50 cases, 168 → 174 AGREE over 204. No other bucket changed.
• FORMAL examples: no expectation churn, so none had captured a projected false for NULL.
• Rust, Python and example suites green. The one SMOKE failure (expander_rewriters query 7) is identical on main.

Scoping

Before editing, every consumer of predicate output was checked:

• the WHERE evaluator already maps NULL to UNKNOWN;
• HAVING's is_truthy treats NULL as not-true, which is correct;
• IIF(NULL, …) already took the false branch.

So nothing downstream had to change.

Commits

1. test(parity): pin simple CASE x WHEN NULL. It isn't a predicate, so the matrix can't see it.
2. fix(r13): the evaluator change, Trilean conversions and their unit test, matrix KNOWN cleared, corpus expects dropped.
3. docs(parity): P48 and P50 closed; R13 slice 2 result recorded.

Not in this slice

• P52: NULL join keys, on both join paths. That's slice 6.
• Case-insensitivity: not yet threaded into this evaluator. That's slice 3, one construction path.
• P51: AND in a SELECT item doesn't parse. A parser fix, outside R13.

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https://claude.ai/code/session_01GpuTexUeuyuAdmDsukMTRW