Prove that logical statement $\phi$ build only with $\leftrightarrow$ is tautology iff every atomic statement of $\phi$ appears even number of times
30306
A is a proposition formula that contains only iff. A is a tautology iff each atomic proposition in A appears an even number of times.
12569
Using the terms 'theorem 'and 'tautology'
87928
Proof of logical equivalence of biconditional and other proposition
122015
"This statement is false" - Propositional Logic
9158
Proving that a propositional theory of any cardinality has an independent set of axioms
91861
Propositional Logic: p → q, ¬p → r, ¬q → ¬r ⊢ q
21035
Clarifying on how if p,q is logically equivalent to p only if q
10598
Contrapositive Fitch Proof
109858
How could a statement be true without proof?
36942
What does it mean that a set S tautologically implies wff $\tau$
102917
Proving statement - $(A \setminus B) \cup (A \setminus C) = B\Leftrightarrow A=B , C\cap B=\varnothing$
155679
If union of two theories is not consistent one of them implies a sentence which the other implies opposite of it
118189
Proving the pairing axiom from the rest of ZF
13074
Prove Logical Equivalence
78356
How to prove ${n \choose p} \equiv\left\lfloor \frac{n}{p} \right\rfloor\pmod p$
76347
Shorter proof for some equvalences
59187
Proof, is $\forall x : (P(x) \lor Q(x)) \Leftrightarrow \forall x : P(x) \lor \forall x : Q(x)$?