Definition:Proof System/Rule of Inference
Let $\LL$ be a formal language.
Part of defining a proof system $\mathscr P$ for $\LL$ is to specify its rules of inference.
Often, the formulation of rules of inference also appeals to the notion of provable consequence.
Also known as
Rules of inference are also known as rules of transformation or transformation rules.
In the context of propositional logic, an example of a rule of inference is:
which expresses Modus Ponendo Ponens.