User BrianO

28 votes

Accepted

Is the negation of a non-theorem a theorem?

answered Nov 7, 2015 at 0:55

23 votes

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Is every relation which is transitive and symmetric also reflexive?

answered Jul 5, 2016 at 16:40

20 votes

Quantifier: "For all sets"

answered Dec 10, 2015 at 4:39

17 votes

Absolute value and max/min function: why $a + b + |a - b|=2\max(a,b)$?

answered Jan 30, 2016 at 12:33

16 votes

Can a set be neither open nor closed?

answered Oct 12, 2015 at 20:16

14 votes

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Inverse of $A^{-1}+B^{-1}$

answered Oct 30, 2015 at 22:32

10 votes

Why is the Axiom of Pairing required?

answered Mar 5, 2022 at 19:55

10 votes

Why is the Axiom of Infinity necessary?

answered Jan 31, 2016 at 3:06

9 votes

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Is there any well-ordered uncountable set of real numbers under the original ordering?

answered Apr 22, 2016 at 18:39

8 votes

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Sum of monotone functions

answered Oct 28, 2015 at 10:04

8 votes

Counterexample, union of intersections, intersection of unions

answered Oct 31, 2015 at 8:51

8 votes

What's the point of allowing only quantification of variables in first-order logic.

answered Apr 17, 2016 at 18:29

8 votes

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Predicate Logic Expression: "Nobody loves anybody."

answered Feb 17, 2016 at 5:22

7 votes

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Logical formula of definition of linearly dependent

answered Nov 10, 2015 at 6:43

7 votes

Is this alternative notion of continuity in metric spaces weaker than, or equivalent to the usual one?

answered Dec 1, 2015 at 4:25

7 votes

Please Explain Kuratowski Definition of Ordered Pairs

answered May 2, 2016 at 4:24

7 votes

$\infty$ and $-\infty$ are to $\aleph_0$ / $\beth_0$ as "what" is to $\beth_1$?

answered Mar 10, 2016 at 3:21

7 votes

Is the set of all topological spaces bigger than the set of all metric space?

answered Feb 5, 2016 at 0:11

7 votes

mathematical symbol for a new member replacing a member in a set

answered Feb 5, 2016 at 14:09

7 votes

Intuitive meaning of the concept “computable”

answered Feb 7, 2016 at 16:22

7 votes

How can a Cauchy sequence converge to an irrational number?

answered Jan 11, 2016 at 3:58

6 votes

Can I use greek letters such as alpha to denote a set?

answered Oct 16, 2015 at 19:01

6 votes

Accepted

Laws of logic Assertion/Reason format

answered Oct 14, 2015 at 6:15

6 votes

Implication in mathematics - How can A imply B when A is False?

answered Oct 11, 2015 at 0:46

6 votes

Differentiable function on an interval containing 0

answered Nov 16, 2015 at 21:07

6 votes

Why might Dieudonne have been "begging the question" by appealing to second-order Peano Axioms?

answered Mar 3, 2016 at 22:26

6 votes

If $f:X\rightarrow Y$ and $V\subseteq Y$, does there exist $U\subseteq X$ such that $f(U)=V$?

answered Jun 8, 2016 at 9:34

6 votes

If a formula $φ$ contains at most one occurrence of any sentence letter, then $φ$ is not a tautology.

answered Feb 2, 2016 at 0:13

6 votes

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Use of directed sets in the definition of nets in topology

answered Jan 23, 2016 at 1:12

5 votes

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Limits of transfinite numbers

answered Oct 6, 2015 at 20:29

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641 Answers

Is the negation of a non-theorem a theorem?

Is every relation which is transitive and symmetric also reflexive?

Quantifier: "For all sets"

Absolute value and max/min function: why $a + b + |a - b|=2\max(a,b)$?

Can a set be neither open nor closed?

Inverse of $A^{-1}+B^{-1}$

Why is the Axiom of Pairing required?

Why is the Axiom of Infinity necessary?

Is there any well-ordered uncountable set of real numbers under the original ordering?

Sum of monotone functions

Counterexample, union of intersections, intersection of unions

What's the point of allowing only quantification of variables in first-order logic.

Predicate Logic Expression: "Nobody loves anybody."

Logical formula of definition of linearly dependent

Is this alternative notion of continuity in metric spaces weaker than, or equivalent to the usual one?

Please Explain Kuratowski Definition of Ordered Pairs

$\infty$ and $-\infty$ are to $\aleph_0$ / $\beth_0$ as "what" is to $\beth_1$?

Is the set of all topological spaces bigger than the set of all metric space?

mathematical symbol for a new member replacing a member in a set

Intuitive meaning of the concept “computable”

How can a Cauchy sequence converge to an irrational number?

Can I use greek letters such as alpha to denote a set?

Laws of logic Assertion/Reason format

Implication in mathematics - How can A imply B when A is False?

Differentiable function on an interval containing 0

Why might Dieudonne have been "begging the question" by appealing to second-order Peano Axioms?

If $f:X\rightarrow Y$ and $V\subseteq Y$, does there exist $U\subseteq X$ such that $f(U)=V$?

If a formula $φ$ contains at most one occurrence of any sentence letter, then $φ$ is not a tautology.

Use of directed sets in the definition of nets in topology

Limits of transfinite numbers