# `Tptp.Lint.Rules.Parent`
[🔗](https://github.com/jcschuster/tptp/blob/v0.1.3/lib/tptp/lint/rules/parent.ex#L1)

An inference record naming a parent absent from the unit.

In a derivation, `inference(rule, [], [a, b])` records that the formula was
derived from `a` and `b`. An absent parent renders the derivation uncheckable,
indicating either a dropped statement or an incorrect name.

A warning, reported only for names occurring in formula-name position. A
`<source>` is a `<dag_source>`, an `<internal_source>`, an `<external_source>`,
the literal `unknown`, or a bracketed list of sources, and `<name>` is reachable
through more than one of these: the rule of an `<inference_record>` and the file
name of a `<file_source>` are not formula names and are not resolved as such.
Neither is the literal `unknown`, which the grammar reads as a `<name>` — the
first of `Tptp.Bnf.Generator`'s departures — and which is therefore never
reported as a missing parent. The rule also declines unless the unit names at
least one formula, so it reports nothing for a problem containing no derivation.

Before v9.3.1.2 a `<source>` was a `<general_term>`, which admitted anything at
all in the position this rule resolves.

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*Consult [api-reference.md](api-reference.md) for complete listing*