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Timo's user avatar
Timo's user avatar
Timo
  • Member for 4 years, 1 month
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3 votes
Accepted

Show that there is always a proposition between two propositions logic

3 votes
Accepted

If $\alpha<\beta$, there exists a ordinal $\gamma$ such that $\alpha + \gamma = \beta$. Why?

3 votes
Accepted

A problem with the Boolos/Burges/Jeffrey proof of incompleteness of second order logic

3 votes

Upward Löwenheim-Skolem Theorem for logics without equality

3 votes
Accepted

In ZFC, why was it chosen to not define what exactly a set or $\epsilon$ relation is?

2 votes

Weakening or strengthening theorems in A Logical Approach to Discrete Math by Gries and Schneider

2 votes
Accepted

Formal proof for conjuction elimination (simplification rule) in natural deduction

2 votes
Accepted

If $\Gamma \vdash \phi$ then $\Gamma[v / c] \vdash \phi[v / c]$

2 votes

Why do we write 'finite' as an adjective to proposition when defining an axiomatic system?

2 votes
Accepted

Prove that $f$ is recursive given that $T\vdash\phi(a,b)$ iff $f(a)=b$

2 votes
Accepted

Interpreting english EITHER-OR when approaching logical deductions doubt

2 votes
Accepted

Specific question about example of Family of sets & Set builder notation

2 votes
Accepted

Does all proofs by contrapositive have a direct proof that is similar in length?

2 votes
Accepted

If we would drop transitivity from intutionistic Kripke frames

2 votes
Accepted

Show $X=\{(x_n)_{n\in\mathbb{N}}\in \mathbb{Z}^{\mathbb{N}}:x_{2i-1}<x_{2i+1} \land x_{2(i+1)}<x_{2i}\ \forall \ i \in \mathbb{N}\}$ is uncountable.

2 votes
Accepted

Is disjunction elimination a more general form of modus ponens?

2 votes
Accepted

Explaining the difference between two definitions for recursively enumerable languages.

2 votes

Predicate Logic - Natural deduction

2 votes

Why do the propositional and first-order logic systems have different choices for their domains?

2 votes
Accepted

Collection of all ordered pairs with fixed first coordinate is a proper class

1 vote
Accepted

Finite fixpoint of the big union operator

1 vote
Accepted

Decidability of a set of universal $\mathcal{L}$-tautologies

1 vote

Russell's paradox and ZFC, "set" vs. "class"

1 vote

If all finite subsets of a set have at most rank W, does the set itself necessarily have at most rank W?

1 vote

Why is the set of well formed formulas are defined as the smallest set of strings

1 vote
Accepted

Prove that $\Sigma\Vdash^g_M \phi$ iff $\{\square^n\sigma: \sigma\in \Sigma,n\in\omega\} \Vdash_M\phi$

1 vote

Set theory task

1 vote
Accepted

Invertibility of inference rules with quantifiers

1 vote

How to determine the logical form of a statement?

1 vote

Resources, references, or examples for logics with finitely many sentences