Classify with an exception

Intent

I want to drop the ordinary qualification when an established exception applies.

The ordinary qualification and its exception are different rules.

Correct formFrozen execution sceneBoundary

Wrong form and why it stays silent

Incorrect form

classification eligible(p: Person) defeater { when young(p); }

A classification must support the class. The exception is written as a separate defeater, not as force defeater on classification.

Correct form

Arxo Law

language "law.core" version "0.2";
package recipes.g.r03 version "0.1.0";
namespace "urn:recipe:g-concepts:03";

entity Person;
relation young(p: Person) kind empirical;
relation exceptional(p: Person);
classification eligible(p: Person) defeasible { when young(p); }
rule Exclude defeater { for p: Person; when exceptional(p); defeat eligible(p); }

Frozen execution scene

Facts on 13.09.2026	Question	Answer
ordinary case	truth(eligible(entity_ref("urn:recipe:g-concepts:03:p")))	truth_status == TRUE_ONLY; / COMPUTED
exception	truth(eligible(entity_ref("urn:recipe:g-concepts:03:p")))	truth_status == NEITHER; / COMPUTED
no ground	truth(eligible(entity_ref("urn:recipe:g-concepts:03:p")))	truth_status == NEITHER; / COMPUTED
defeater removed	truth(eligible(entity_ref("urn:recipe:g-concepts:03:p")))	truth_status == TRUE_ONLY; / COMPUTED

ordinary case classifies

Arxo Law

test "ordinary case classifies" {
    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 young(entity_ref("urn:recipe:g-concepts:03:p"));
    }
    evaluate truth(eligible(entity_ref("urn:recipe:g-concepts:03:p")));
    expect truth_status == TRUE_ONLY;
    expect evaluation_status == COMPUTED;
}

exception defeats classification

Arxo Law

test "exception defeats classification" {
    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 young(entity_ref("urn:recipe:g-concepts:03:p")); assert exceptional(entity_ref("urn:recipe:g-concepts:03:p"));
    }
    evaluate truth(eligible(entity_ref("urn:recipe:g-concepts:03:p")));
    expect truth_status == NEITHER;
    expect evaluation_status == COMPUTED;
}

no ground stays unknown

Arxo Law

test "no ground stays unknown" {
    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 exceptional(entity_ref("urn:recipe:g-concepts:03:p"));
    }
    evaluate truth(eligible(entity_ref("urn:recipe:g-concepts:03:p")));
    expect truth_status == NEITHER;
    expect evaluation_status == COMPUTED;
}

removed defeater restores classification

Arxo Law

test "removed defeater restores classification" {
    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 young(entity_ref("urn:recipe:g-concepts:03:p")); assert exceptional(entity_ref("urn:recipe:g-concepts:03:p"));
    }
    evaluate truth(eligible(entity_ref("urn:recipe:g-concepts:03:p")));
    expect truth_status == TRUE_ONLY;
    expect evaluation_status == COMPUTED;
}

Counterfactual

Mutation classification eligible(p: Person) defeasible → classification eligible(p: Person) defeater: LDC-E0201.

Boundary

A defeater removes support but does not prove not eligible. A strict classification is not cancelled by the same exception.