LDC-E1368 — Assertions contradicting a key

What it means

A relation can declare a key: the parameters that identify a row. Two assertions under the same key value must then agree — the same key, the same tuple. When the package’s own assertions yield different tuples under one key in overlapping applicability windows, the table contradicts itself, and no later reasoning can decide which row holds. The compiler stops at the second row.

The repair is to keep one row, or to separate the rows so their windows no longer overlap. A key promises one answer per value; the assertions must keep that promise.

Example

Arxo Law

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

relation koef(klass: Text, value: Decimal) kind empirical {
    key(klass);
}
assert koef("K0", 2.30);
assert koef("K0", 1.55);

Fix

Arxo Law

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

relation koef(klass: Text, value: Decimal) kind empirical {
    key(klass);
}
assert koef("K0", 2.30);

Engine message

The engine reports this in its own wording:

Output

example.law:9:1: error LDC-E1368: relation koef: the package's own assertions yield different tuples under the same projection onto key(klass) = ("K0") and overlapping §92 applicability windows — the table contradicts its key (SPEC §45.1/§196, errata E-0210); separate the rows by edition or keep one

Related

• Facts and evidence — asserting what holds.