can deductive system be strongly sound without being sound
63963
deductive system where the axioms are all the propositions that are not tautology
108155
How can we justify the use of logic?
107888
Why zero correlation does not necessarily imply independence
99168
Does Hilbert's $\varepsilon$-calculus have any real problem when using for incomplete systems?
93742
Show that the conditional statement is a tautology without using a truth table
43700
Are proofs by contradiction really logical?
48368
Prove using Natural Deduction in predicate logic $(\forall x\ P(x))\to Q ⊢ \exists x (P(x)\to Q)$
4700
Can paraconsistent or other logics make the impossible happen?
32950
Fake induction proofs
42777
Is it possible to know anything with certainty?
142382
Is "logicalising" a valid word?
122684
How do you prove Well-Ordering without Mathematical Induction? (and vice-versa)
79727
Direct proof of non-flatness
140194
Using natural deduction to prove that $p \implies q \vdash \lnot p \lor q$
41318
Can every proof by contradiction also be shown without contradiction?
68607
Could an argument with false Premises and a true Conclusion be logically valid?
123458
Prove $( \lnot C \implies \lnot B) \implies (B \implies C)$ without the Deduction Theorem