LDC-E4104 — A priority cycle between rules

For LLMs5 sections

What it means

Priorities order defeasible rules: one rule preferred over another wins their conflict. That order must itself be acyclic — a rule preferred over its rival, which is in turn preferred over the first, leaves no rule on top and no conflict resolved. The compiler refuses the cycle where the closing edge lands.

The fix drops or reverses one edge of the loop so the order runs one way. A single edge between two conflicting rules, and edges that never close into a loop, stay silent.

Example

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 D2 defeasible { for x: Text; when q(x); then not p(x); }
rule S1 strict { for x: Text; when q(x); then r(x); }
priority P1 { prefer D1 over D2; }
priority P2 { prefer D2 over D1; }

Fix

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 D2 defeasible { for x: Text; when q(x); then not p(x); }
rule S1 strict { for x: Text; when q(x); then r(x); }
priority P1 { prefer D1 over D2; }

Engine message

The engine reports this in its own wording:

example.law:11:10: error LDC-E4104: static priority cycle between rules [D1, D2] — error in executable profile (§192/§106)

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