Factor Principles/Disjunction on Left/Formulation 2

Theorem

 * $\vdash \left({p \implies q}\right) \implies \left({\left({r \lor p}\right) \implies \left ({r \lor q}\right)}\right)$

Also see

 * This is an axiom of the following proof system:
 * Definition:Hilbert Proof System/Instance 2