# LDC-E1304 — Relation key names an undeclared parameter

## What it means

A relation key lists the parameters that identify each row: every name
in the key must be a parameter the relation itself declares. A key that
names something the parameter list never introduced points at nothing,
so the compiler stops at the unknown name.

The repair is a spelling check against the parameter list: fix the
typo, declare the missing parameter, or drop the name from the key.
The key keeps only what the relation declares.

## Example

```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 {
    key(y);
}
```

## Fix

```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 {
    key(x);
}
```

## Engine message

The engine reports this in its own wording:

```text
example.law:6:9: error LDC-E1304: key(y): parameter is not declared in relation "p" (§45.1)
```

## Related

- [Vocabulary](/constructs/vocabulary/) — how names are declared and which positions take them.