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General rule with an exception

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# General rule with an exception

## Intention

I want to lift a general rule by carrying the bound person into the exception itself.

A person bound only in the general rule body is not automatically bound in the exception.

## Incorrect form and why it stays silent

```text title="Incorrect form"
unless lost(item);
```

The general-rule body is not carried into the exception: p remains an unbound variable of the generated defeater.

## Correct form

```law
language "law.core" version "0.2";
package recipes.b.r01 version "0.1.0";
namespace "urn:recipe:b-rules:01";

entity Person;
entity Item;
relation owns(p: Person, item: Item);
relation lost(item: Item);
relation allowed(p: Person, item: Item);
rule General defeasible {
    for p: Person; for item: Item;
    when owns(p, item);
    then allowed(p, item);
    unless owns(p, item) and lost(item);
}
```

## Frozen execution scene

| Facts and choice | Question | Answer |
|---|---|---|
| item with the owner | `truth(allowed(entity_ref("urn:recipe:b-rules:01:p"), entity_ref("urn:recipe:b-rules:01:a")))` | `TRUE_ONLY` / `COMPUTED` |
| item lost | `truth(allowed(entity_ref("urn:recipe:b-rules:01:p"), entity_ref("urn:recipe:b-rules:01:a")))` | `NEITHER` / `COMPUTED` |
| proviso removed | `truth(allowed(entity_ref("urn:recipe:b-rules:01:p"), entity_ref("urn:recipe:b-rules:01:a")))` | `TRUE_ONLY` / `COMPUTED` |

```law
test "item with owner" {
    given {
        context {
            legal_time @2026-09-13;
            decision_time @2026-09-13T09:00:00+05:00;
            knowledge_time @2026-09-13T09:00:00+05:00;
            timezone "Asia/Almaty";
        }
        assert owns(entity_ref("urn:recipe:b-rules:01:p"), entity_ref("urn:recipe:b-rules:01:a"));
    }
    evaluate truth(allowed(entity_ref("urn:recipe:b-rules:01:p"), entity_ref("urn:recipe:b-rules:01:a")));
    expect truth_status == TRUE_ONLY;
    expect evaluation_status == COMPUTED;
}
```

```law
test "item lost" {
    given {
        context {
            legal_time @2026-09-13;
            decision_time @2026-09-13T09:00:00+05:00;
            knowledge_time @2026-09-13T09:00:00+05:00;
            timezone "Asia/Almaty";
        }
        assert owns(entity_ref("urn:recipe:b-rules:01:p"), entity_ref("urn:recipe:b-rules:01:a")); assert lost(entity_ref("urn:recipe:b-rules:01:a"));
    }
    evaluate truth(allowed(entity_ref("urn:recipe:b-rules:01:p"), entity_ref("urn:recipe:b-rules:01:a")));
    expect truth_status == NEITHER;
    expect evaluation_status == COMPUTED;
}
```

```law
test "exception removed" {
    given {
        context {
            legal_time @2026-09-13;
            decision_time @2026-09-13T09:00:00+05:00;
            knowledge_time @2026-09-13T09:00:00+05:00;
            timezone "Asia/Almaty";
        }
        assert owns(entity_ref("urn:recipe:b-rules:01:p"), entity_ref("urn:recipe:b-rules:01:a")); assert lost(entity_ref("urn:recipe:b-rules:01:a"));
    }
    evaluate truth(allowed(entity_ref("urn:recipe:b-rules:01:p"), entity_ref("urn:recipe:b-rules:01:a")));
    expect truth_status == TRUE_ONLY;
    expect evaluation_status == COMPUTED;
}
```

## Counterfactual

Mutation: `unless owns(p, item) and lost(item);` → `unless lost(item);`; rejection LDC-E4101. Scenes that delete a fragment are marked explicitly in the table.

## Boundary

A bare unless blocks the conclusion rather than establishing its negation. The contrary form is [An exception establishes negation](/recipes/b-rules/contrary-exception/).

## Pitfall

Bind the same person in the exception: a variable bound only in the general rule body stays unbound in the generated defeater.