A rule not used in propositional logic. It goes like this:

(P>Q) * (R>S)

~Q ^ ~S

Therefore, ~P ^ ~R

*
"If is rains (P), then you'll get wet (Q)" and "If it's cold, then you'll shiver"*

Either you're not wet, or you're not shivering.

Therefore, either it's not raining, or it's not cold.

You can turn it into a Constructive Dilemma by using Transposition. Constructive Dilemma is a perfectly fine logical rule. Hence Destructive Dilemma is valid, is simply isn't used. This is simply because it would be redundant to have both Constructive Dilemma and Destructive Dilemma.

Key:

> = If, Then

* = And

~ = Not

^ = Or

P, Q, R, S = Statements