Deduction theorem for Natural Deduction
131257
$\to$ vs. $\vdash$ in logic
5098
Theorem without numbering
128111
Why is a deductive closure an intersection of maximally consistent sets?
10598
Contrapositive Fitch Proof
65379
Deriving $\neg R$ from $\{R↔(R∨(P∧¬P)), R↔¬P, ¬P→(P↔(Q→Q)), P→Q\}$
42869
Is $\lor$ definable in intuitionistic logic?
126713
Strong induction and vacuous truth
150451
Logic soundness and completeness
83037
Applying Zorn's Lemma to natural numbers
27600
Gödel's (in)completeness theorems and the axiomatization of Euclidean geometry
75007
How can I prove this relation between the elementary set theory and the elementary logic?
16187
proof of functional completeness of logical operators
3217
Construction of uncountably many non-isomorphic linear (total) orderings of natural numbers
122184
De Morgan's laws in logic and set theory
84562
Proof using only field axioms
147947
Does double negation distribute over implication intuitionistically?
62936
Proving equivalencies of two versions of the Axiom of Choice