An Etymological Dictionary of Astronomy and Astrophysics
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i) If t₁, t₂, ..., t_n are terms and P is a → predicate of arity n, then P(t₁, t₂, ..., t_n) is an atomic wff.
ii) If t₁ and t₂ are terms, then (t₁ = t₂) is an atomic wff.

→ atomic; → wff.

In → predicate logic, a → wff with no → free occurrences of any → variable. Also called a → sentence.

→ closed; → wff.

In → predicate logic, a → well-formed formula with one or more → free occurrences of → variables.

→ open; → wff.

A string of → symbols from the alphabet of the → formal language that conforms to the grammar of the formal language. → closed wff, → open wff.

Wff, pronounced whiff; → well; → form; → formula.