Here follows a set of twenty elementary valid arguments. They are valid because each of them is exactly in the form of one of the nine elementary valid argument forms. For each of them, state the rule of inference by which its conclusion follows from its premise or premises.

(P₁): (W ⋅ ∼X) ≡ (Y ⊃ Z)
∴ [(W ⋅ ~ X) ≡ (Y  ⊃ Z)] ꓦ (X ≡ ~ Z)