Given p ⇒ q, use the Fitch System to prove ¬q ⇒ ¬p.
65486
Contraposition and law of excluded middle
48368
Prove using Natural Deduction in predicate logic $(\forall x\ P(x))\to Q ⊢ \exists x (P(x)\to Q)$
22193
Why, logically, is proof by contradiction valid?
5293
Show that the logic $ \ \forall x \exists y \ P(x,y) \ $ is not logically equivalent to $ \ \exists x \forall y \ P(x,y) \ $
37183
Show that the set of all $x$ such that $x \in P$ and $x \notin Q$ exists
147375
Prove :(P → Q) ∨ (Q → P) using natural deduction
23869
Prove the implication "if $ac>bc$ and $c>0$, then $a>b$" using the contrapositive
157625
How to prove conditional in Coq?
152856
Using $p\supset q$ instead of $p\implies q$
93557
Intuitively, why does (B → S) ≡ (¬B ∨ S)?
144396
fitch style proof problem regarding rule of inferences
15354
Formal proof of $\exists x \forall y P(x,y) \implies \forall y \exists x P(x,y)$
6119
If both $P$ and $Q$ are true , how can I tell that $P$ implies $Q$?
32244
Propositional Logic - Deduction
129185
Understanding the truth value for ⇏ when antecedent is false and consequent is true.
61671
Discrete Math: Writing Proofs
32009
Prove $\;\big((p\rightarrow q) \lor (p \rightarrow r)\big) \rightarrow (q\lor r)\equiv p \lor q \lor r$ without use of a truth table.