Proof of a theorem in first order logic using indirect proof
1027
Why is this true? $(\exists x)(P(x) \Rightarrow (\forall y) P(y))$
153975
Proving mathematical induction with arbitrary base using (weak) induction
31722
Prove $-(-a)=a$ using only ordered field axioms
76347
Shorter proof for some equvalences
104871
Direct cut-elimination for natural deduction.
91861
Propositional Logic: p → q, ¬p → r, ¬q → ¬r ⊢ q
13074
Prove Logical Equivalence
145759
formal proof from calulus
82739
Why is $\alpha \rightarrow \forall x(\alpha)$ not generally correct in first-order logic?
134588
Seeking a direct proof about nested inclusions
151356
Need Hints Prove "$((\neg \alpha \to \alpha) \to \alpha) $" Using Axiom 1,2,3 and MP and deduction theorem
21254
Formal language: Proving the reverse operation on a word through induction
114550
Well-ordering theorem and second-order logic
138632
Proof that if $a > 0$, then $\frac{1}{a} > 0$ using just field and order axioms
15354
Formal proof of $\exists x \forall y P(x,y) \implies \forall y \exists x P(x,y)$
158295
First Order Logic clauses decidability
87257
How to prove this sequent using natural deduction?