LDC-E4105 — A priority over a strict rule

What it means

Priorities run between defeasible rules only: strict rules state logical consequences, not preferences, and no ordering can prefer one consequence over another. Naming a strict rule on either side of a priority edge asks the ordering to do what the category forbids. The compiler refuses the edge at the priority.

The fix takes the strict rule out of the edge — restate the choice between defeasible rules, or drop the edge if the strict conclusion was meant to stand unconditionally. Edges between two defeasible rules stay silent.

Example

Arxo Law

language "law.core" version "0.2";
package demo.diagnostics version "0.1.0";
namespace "urn:law:demo:diagnostics";

relation p(x: Text) kind institutional;
relation q(x: Text) kind institutional;
relation r(x: Text) kind institutional;
rule D1 defeasible { for x: Text; when q(x); then p(x); }
rule S1 strict { for x: Text; when q(x); then r(x); }
priority P1 { prefer S1 over D1; }

Fix

Arxo Law

language "law.core" version "0.2";
package demo.diagnostics version "0.1.0";
namespace "urn:law:demo:diagnostics";

relation p(x: Text) kind institutional;
relation q(x: Text) kind institutional;
relation r(x: Text) kind institutional;
rule D1 defeasible { for x: Text; when q(x); then p(x); }
rule S1 strict { for x: Text; when q(x); then r(x); }

Engine message

The engine reports this in its own wording:

Output

example.law:10:10: error LDC-E4105: priority over strict rule "S1" — error (§192/§114: strict is a logical category, priorities run between defeasible)

Related

• Priority — how conflicts between rules are settled.
• Strict rules — how a strict rule reads its body.