How to explain that $A \implies B$ is true when $A$ is false
578
In classical logic, why is $(p\Rightarrow q)$ True if both $p$ and $q$ are False?
132971
Prove that $|a| < b \iff -b<a<b$
151038
How to prove (A v B), (A → C), (B → D) therefore (C v D)
67717
$A \oplus B = A \oplus C$ imply $B = C$?
20462
Validity of conditional statement when the premise is false.
155884
What are the conditions on $\text{tr}(AB) \leq \text{tr(A)} \text{tr(B)}$ to be true?
42590
Understanding implication in logic truth tables (excerpt from textbook)
20789
If $\Sigma \vdash \varphi$ then $\Sigma \vdash \forall x \varphi$. Why when $(\varphi \implies \forall x \varphi)$ is not true?
109858
How could a statement be true without proof?
56399
Proof for $A \cup B = B$ if and only if $A \subset B$
83714
$A \in B$ vs. $A \subset B$ for proofs
113735
Do we need to prove that if x∉A in proposition "if A⊆B then A⋃B=B"?
105303
'Obvious' theorems that are actually false
21737
If $A|B$ and $B|A$ then prove $A=\pm B$
111763
True or False $A - C = B - C $ if and only if $A \cup C = B \cup C$
46831
Show that $ a，b, \sqrt{a}+ \sqrt{b} \in\mathbb Q \implies \sqrt{a},\sqrt{b} \in\mathbb Q $
77859
Prove or find a counter example to the claim that for all sets A,B,C if A ∩ B = B ∩ C = A ∩ C = Ø then A∩B∩C ≠ Ø