How exactly are we proving that modus ponens is valid?
47222
Soundness of a rule of a proof system with respect to the truth tables?
29204
$a\equiv\bar a\!\pmod{\!kn}\Rightarrow a\equiv\bar a\!\pmod{\! n};\ $ $(a\bmod kn)\bmod n=a\bmod n.\ $ Congruences persist mod factors of the modulus
32441
How to prove or disprove statements about sets
9282
Prove using natural deduction $((P \land Q) \rightarrow R) \vdash (P \rightarrow R) \lor (Q\rightarrow R)$
32325
Can there be a valid argument which has a tautology as a conclusion?
22584
Can we prove that a statement cannot be proved?
106799
Proof Verification: Converse of Intermediate Value Theorem
144266
set theory proof of $A\cap B = A \setminus(A\setminus B)$
154406
Real analysis - proof approach help
29231
Proof of : $x^{n}\equiv x^{\varphi(m)+[n \bmod \varphi(m)]} \mod m$
134049
Showing an inequality is valid
59964
Why an inconsistent formal system can prove everything?
145466
Is this a valid mathematical proof?
134588
Seeking a direct proof about nested inclusions
89796
How should I prove the duality?
43700
Are proofs by contradiction really logical?
109685
An invalid argument, the conclusion of which is a tautology