User Chris Eagle

97 votes

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Given a simple graph and its complement, prove that either of them is always connected.

answered Mar 19, 2012 at 18:49

96 votes

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Why is $\mathbb{Z}[\sqrt{-n}], n\ge 3$ not a UFD?

answered Oct 8, 2011 at 23:58

79 votes

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Rational number to the power of irrational number = irrational number. True?

answered Jul 22, 2013 at 12:45

65 votes

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Finitely generated module with a submodule that is not finitely generated

answered Mar 27, 2012 at 10:41

60 votes

How to prove that the number $1!+2!+3!+...+n!$ is never square?

answered Apr 19, 2011 at 18:10

57 votes

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Is it true that a space-filling curve cannot be injective everywhere?

answered Jun 3, 2011 at 22:45

54 votes

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A natural number multiplied by some integer results in a number with only ones and zeros

answered Nov 20, 2011 at 13:45

39 votes

Getting the sequence $\{1, 0, -1, 0, 1, 0, -1, 0, \ldots\}$ without trig?

answered Apr 11, 2012 at 19:03

36 votes

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Application of the Sylow Theorems to groups of order $p^2q$

answered Aug 16, 2011 at 23:56

33 votes

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Are the functions $\sin^n(x)$ linearly independent?

answered May 31, 2012 at 18:21

32 votes

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A finite, cancellative semigroup is a group

answered Sep 26, 2012 at 20:19

29 votes

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How do I prove that $\cos{\frac{2\pi}{7}}\notin\mathbb{Q}$?

answered Oct 11, 2011 at 12:36

27 votes

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entire bijection of $\mathbb{C}$ with 2 fixed points

answered May 16, 2011 at 19:56

27 votes

Fundamental group of $S^2$ with north and south pole identified

answered Feb 3, 2011 at 19:40

27 votes

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A subgroup such that every left coset is contained in a right coset.

answered Jan 20, 2013 at 20:56

26 votes

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Example of nested closed balls with empty intersection?

answered Sep 24, 2012 at 12:38

24 votes

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Why is the ratio test for $L=1$ inconclusive?

answered Apr 17, 2011 at 9:34

23 votes

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Why can't we just say 1 instead of "unity"?

answered Apr 2, 2013 at 21:38

22 votes

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In a monoid, does $x \cdot y=e$ imply $y \cdot x=e$?

answered Oct 18, 2012 at 7:13

20 votes

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the cube of integer can be written as the difference of two square

answered Feb 23, 2012 at 20:16

20 votes

Accepted

Empty set does not belong to empty set

answered Feb 13, 2013 at 11:07

20 votes

equivalent norms in Banach spaces of infinite dimension

answered Jun 20, 2013 at 19:36

19 votes

Every closed set in $\mathbb R^2$ is boundary of some other subset

answered May 29, 2012 at 19:21

19 votes

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Shorter proof of $R/I$ is a field if and only if $I$ is maximal

answered May 19, 2012 at 14:11

18 votes

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How to convert an English sentence that contains "Exactly two" or "Atleast two" into predicate calculus sentence?

answered May 1, 2012 at 13:16

18 votes

Is $\mathbb{R}$ a vector space over $\mathbb{C}$?

answered Jun 6, 2012 at 23:13

18 votes

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Collection of continuous functions determines the topology

answered Jun 13, 2012 at 10:52

17 votes

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Function whose image of every open interval is $(-\infty,\infty)$

answered Aug 24, 2012 at 18:50

17 votes

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Is there an easy example of a vector space which can not be endowed with the structure of a Banach space

answered Oct 19, 2011 at 20:22

17 votes

Accepted

Is the Minkowski sum of a compact set and a closed set necessarily closed?

answered Nov 11, 2011 at 0:10

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408 Answers

Given a simple graph and its complement, prove that either of them is always connected.

Why is $\mathbb{Z}[\sqrt{-n}], n\ge 3$ not a UFD?

Rational number to the power of irrational number = irrational number. True?

Finitely generated module with a submodule that is not finitely generated

How to prove that the number $1!+2!+3!+...+n!$ is never square?

Is it true that a space-filling curve cannot be injective everywhere?

A natural number multiplied by some integer results in a number with only ones and zeros

Getting the sequence $\{1, 0, -1, 0, 1, 0, -1, 0, \ldots\}$ without trig?

Application of the Sylow Theorems to groups of order $p^2q$

Are the functions $\sin^n(x)$ linearly independent?

A finite, cancellative semigroup is a group

How do I prove that $\cos{\frac{2\pi}{7}}\notin\mathbb{Q}$?

entire bijection of $\mathbb{C}$ with 2 fixed points

Fundamental group of $S^2$ with north and south pole identified

A subgroup such that every left coset is contained in a right coset.

Example of nested closed balls with empty intersection?

Why is the ratio test for $L=1$ inconclusive?

Why can't we just say 1 instead of "unity"?

In a monoid, does $x \cdot y=e$ imply $y \cdot x=e$?

the cube of integer can be written as the difference of two square

Empty set does not belong to empty set

equivalent norms in Banach spaces of infinite dimension

Every closed set in $\mathbb R^2$ is boundary of some other subset

Shorter proof of $R/I$ is a field if and only if $I$ is maximal

How to convert an English sentence that contains "Exactly two" or "Atleast two" into predicate calculus sentence?

Is $\mathbb{R}$ a vector space over $\mathbb{C}$?

Collection of continuous functions determines the topology

Function whose image of every open interval is $(-\infty,\infty)$

Is there an easy example of a vector space which can not be endowed with the structure of a Banach space

Is the Minkowski sum of a compact set and a closed set necessarily closed?