Prove tautology without truth using a truth table.
93742
Show that the conditional statement is a tautology without using a truth table
53056
natural deduction: introduction of universal quantifier and elimination of existential quantifier explained
140194
Using natural deduction to prove that $p \implies q \vdash \lnot p \lor q$
75007
How can I prove this relation between the elementary set theory and the elementary logic?
122015
"This statement is false" - Propositional Logic
123458
Prove $( \lnot C \implies \lnot B) \implies (B \implies C)$ without the Deduction Theorem
121720
Given ∃x.¬p(x), use the Fitch System to prove ¬∀x.p(x).
32244
Propositional Logic - Deduction
121361
Showing that $\lnot Q \lor (\lnot Q \land R) = \lnot Q$ without a truth table
147375
Prove :(P → Q) ∨ (Q → P) using natural deduction
127733
How to prove De Morgan’s laws without using contradictions
141814
Proofs using theorems instead of axioms
93410
How to prove ~ (~P & ~Q) : P ∨ Q by natural deduction
140682
Proving a property of a Logic Formal Language
105303
'Obvious' theorems that are actually false
118480
Is modus ponens a tautology?
50178
\qed for theorems without proofs