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LDC-Q2005 — The expression names a variable the query never bound

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# LDC-Q2005 — The expression names a variable the query never bound

## What it means

Inside a filter or a return list, every name must come from somewhere: a
source introduced at the head of the query. A name with no source is not
an empty value and not a typo the engine will guess past — the expression
cannot be evaluated for any row, so the query stops at the first row that
reaches it.

Bind the name in a source, or replace it with the source variable the
expression was meant to read.

## Example

Both queries below run against this package:

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

entity Applicant;
relation resident(a: Applicant) kind institutional;
relation permit_eligible(a: Applicant) kind institutional;

rule PermitEligibility strict {
    for a: Applicant;
    when resident(a);
    then permit_eligible(a);
}
```

The filter reads a name no source introduces:

```lawql
from r in rules where zzz == 1 select r
```

## Fix

```lawql
from r in rules select r
```

## Engine message

The engine reports this in its own wording:

```text
LDC-Q2005: variable 'zzz' is not bound.
```

## Related

- [Questions to the engine](/constructs/queries/) — how sources bind names.
- [LDC-Q2007](/diagnostics/LDC-Q2007/) — when the name exists but the field does not.