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user10389
  • Member for 13 years
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455 votes
23 answers
92k views

Proofs that every mathematician should know. [closed]

32 votes
9 answers
7k views

Which simple puzzles have fooled professional mathematicians?

15 votes
2 answers
35k views

The limit of a product of functions equals the product of the limits: Is this proof rigorous?

9 votes
0 answers
1k views

What is the history of "only if" in mathematics?

9 votes
1 answer
821 views

Who introduced the term "norm" into mathematics?

7 votes
3 answers
3k views

Does every continuous function have a left and right derivative?

6 votes
2 answers
4k views

What did Simon Norton do after 1985?

5 votes
1 answer
732 views

Why is the × operator not defined for vector × vector?

5 votes
3 answers
9k views

Changing variables in a partial derivative

5 votes
2 answers
851 views

How should the Calculus of Variations deal with $\delta(t-t_0)$ variations?

4 votes
1 answer
153 views

Is invariance of a multi-linear form required for co/contra variance?

4 votes
2 answers
722 views

Is a topological space with a Minkowsi metric a topological manifold?

3 votes
2 answers
561 views

What strategy do you use when solving vector equations involving $\nabla$?

3 votes
1 answer
187 views

Is there a lower dimensional vector operator analogous to Curl or Div?

2 votes
1 answer
86 views

What does this infinitesimal Eulerian change describe?

1 vote
2 answers
594 views

Is this a correct definition of a line integral?

1 vote
3 answers
217 views

Some questions on $\frac{\partial f}{\partial x} + \frac{\partial f}{\partial y}+\frac{\partial f}{\partial z} = g(x,y,z)$

1 vote
1 answer
1k views

How is an angle function defined for a manifold?

1 vote
1 answer
214 views

Does Euler's homogenous function theorem hold for functions homogenous in some of its independent variables?

1 vote
1 answer
354 views

Why do we need topological distinctiveness if the points in the set of a topological space are distinct to start with?

1 vote
1 answer
97 views

Is this a correct definition of the Cartesian Product?

1 vote
0 answers
38 views

Must the definition of the limit of a complex function be an inequality?

1 vote
0 answers
104 views

Can the Euler-Lagrange equations be derived from a variation over a time of order $dt$ rather than $t$?

1 vote
0 answers
354 views

what's a homogeneous transformation?

1 vote
1 answer
63 views

Is a linear transformation just a mathematical description of a straight line?

0 votes
0 answers
57 views

How has the definition of a tensor changed since Tullio Levi-Civita's definition?

0 votes
1 answer
24 views

How does $|g(z)-k|<1/2|k|\Rightarrow |g(z)|>1/2|k|?$

0 votes
2 answers
134 views

What's meant by "a family $\{A_i\}$ of subsets of $X$"