An instance of a schema is a sentence obtained from the schema by consistently replacing all metavariables by ordinary expressions. For example, the sentence (p ⇒ (q ∧ r ⇒ p)) is an instance of the schema (φ ⇒ (ψ ⇒ φ)).
An instance of a rule of inference is a rule of inference obtained by consistently replacing all metavariables by ordinary expressions.
|