An exception establishes negation

Intention

I want an explicit refusal, not merely the removal of positive support.

The scenes compare the bare and the contrary forms.

Correct formFrozen execution sceneBoundary

Incorrect form and why it stays silent

Incorrect form

unless special(p);

then duty Stay { bearer p; goal maintenance { condition allowed(p); window [@2026-01-01, infinity); } };
unless special(p) then not allowed(p);

A bare proviso yields NEITHER, a contrary one — FALSE_ONLY. The negation attaches to the literal, not to a duty template. The mutation replaces the literal head with a norm and is rejected with E1302.

Correct form

Arxo Law

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

entity Person;
relation eligible(p: Person);
relation special(p: Person);
relation allowed(p: Person);
rule General defeasible {
    for p: Person; when eligible(p); then allowed(p);
    unless special(p) then not allowed(p);
}

Frozen execution scene

Facts and choice	Question	Answer
explicit refusal	truth(allowed(entity_ref("urn:recipe:b-rules:03:p")))	FALSE_ONLY / COMPUTED
contrary head removed	truth(allowed(entity_ref("urn:recipe:b-rules:03:p")))	NEITHER / COMPUTED
no exception	truth(allowed(entity_ref("urn:recipe:b-rules:03:p")))	TRUE_ONLY / COMPUTED

explicit refusal

Arxo Law

test "explicit refusal" {
    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 eligible(entity_ref("urn:recipe:b-rules:03:p")); assert special(entity_ref("urn:recipe:b-rules:03:p"));
    }
    evaluate truth(allowed(entity_ref("urn:recipe:b-rules:03:p")));
    expect truth_status == FALSE_ONLY;
    expect evaluation_status == COMPUTED;
}

contrary head removed

Arxo Law

test "contrary head 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 eligible(entity_ref("urn:recipe:b-rules:03:p")); assert special(entity_ref("urn:recipe:b-rules:03:p"));
    }
    evaluate truth(allowed(entity_ref("urn:recipe:b-rules:03:p")));
    expect truth_status == NEITHER;
    expect evaluation_status == COMPUTED;
}

no exception

Arxo Law

test "no exception" {
    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 eligible(entity_ref("urn:recipe:b-rules:03:p"));
    }
    evaluate truth(allowed(entity_ref("urn:recipe:b-rules:03:p")));
    expect truth_status == TRUE_ONLY;
    expect evaluation_status == COMPUTED;
}

Counterfactual

Mutation: then allowed(p); → then duty Stay { Bearer p; goal maintenance { condition allowed(p); window [@2026-01-01, infinity); } };; rejection LDC-E1302. Scenes that delete a fragment are marked explicitly in the table.

Boundary

Norm-heads have no complement: unless C then not A is undefined for a position. For conflicting positions, see Two incompatible duties.