User Peter LeFanu Lumsdaine - Mathematics Stack Exchange

4 votes

Relative cell complexes in the undercategory $B/\mathscr{M}$ are relative cell complexes in $\mathscr{M}$ - why must we also assume $B$ is a complex?

answered Feb 7, 2023 at 21:10

4 votes

Accepted

Proof that axiom of replacement won't generate a set going arbitrarily high in the cumulative hierarchy, without relying on replacement?

answered Feb 10, 2023 at 10:14

3 votes

Is there such a thing as a vector without a basis?

answered Jun 10, 2023 at 13:33

3 votes

How does this definition of a topology on $X$ not cause $X \in X$?

answered Aug 19, 2022 at 11:37

3 votes

Show that all roots of a Polynomial must be real numbers

answered Oct 21, 2020 at 14:22

3 votes

Why is addition defined, and not implied, on quotient spaces?

answered Feb 16, 2022 at 12:58

3 votes

Relationship structure homomorphisms vs. category morphisms

answered Apr 18, 2021 at 14:22

3 votes

How to understand the object in a category

answered Dec 21, 2020 at 16:01

3 votes

How to prove the two answers to an integral are equivalent

answered Mar 22 at 18:53

3 votes

What is semantics of "type"? Do "types" of "type theory" semantically differ from "set" of set theory?

answered Jul 3, 2014 at 10:57

3 votes

Accepted

Algebraic transformation for dependent type

answered Mar 24, 2019 at 22:44

3 votes

Is the opposite functor full and bijective on objects?

answered Nov 18, 2016 at 9:59

3 votes

Accepted

Prove that the class of well-founded sets is a proper class

answered Jun 3, 2013 at 5:34

2 votes

Accepted

Abelian-by-abelian group

answered May 9, 2013 at 14:51

2 votes

For every closed set $C$, $f^{-1}(C)$ is closed. Is $f$ necessarily continuous?

answered Dec 7, 2012 at 20:52

2 votes

sequence $2,10,18,26,$.... contains no cube

answered Jun 16, 2013 at 15:16

2 votes

Algebraic formula for co-products in the category of digraphs

answered Sep 9, 2013 at 18:36

2 votes

What is the name of a function that changes the sign of a number?

answered Nov 21, 2011 at 22:04

2 votes

what is the speed of a divergent series?

answered Jan 13, 2011 at 5:51

2 votes

Elevator pitch for a (sub)field of maths?

answered Oct 15, 2010 at 15:20

2 votes

What Does the Associative Property Mean Intuitively Across All Notational Schemes?

answered Jun 12, 2013 at 21:34

2 votes

Accepted

Examples of (co)complete 2-categories that aren't (co)complete as a 1-category

answered Aug 3, 2016 at 19:02

2 votes

Accepted

Torus/ Thick Möbius Band homeomorphism

answered Nov 25, 2014 at 10:36

2 votes

Is a constant such as 8 considered an expression?

answered Apr 23, 2014 at 3:06

2 votes

Where is the value of the variable $\epsilon$ obtained in the following explanation my professor gave?

answered Oct 22, 2013 at 3:31

2 votes

Is this a valid example for $f \circ g = id_M$, but $g \circ f \ne id_N$

answered Oct 22, 2013 at 16:06

2 votes

Is there a geometric realization of Quaternion group?

answered Aug 17, 2021 at 19:25

2 votes

Are these bases for a topology?

answered Oct 22, 2013 at 19:53

2 votes

Powerset functor weakly preserves pullbacks.

answered Dec 8, 2013 at 20:56

2 votes

Is a Lattice just a linearly ordered set?

answered Dec 21, 2013 at 18:35

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116 Answers

Relative cell complexes in the undercategory $B/\mathscr{M}$ are relative cell complexes in $\mathscr{M}$ - why must we also assume $B$ is a complex?

Proof that axiom of replacement won't generate a set going arbitrarily high in the cumulative hierarchy, without relying on replacement?

Is there such a thing as a vector without a basis?

How does this definition of a topology on $X$ not cause $X \in X$?

Show that all roots of a Polynomial must be real numbers

Why is addition defined, and not implied, on quotient spaces?

Relationship structure homomorphisms vs. category morphisms

How to understand the object in a category

How to prove the two answers to an integral are equivalent

What is semantics of "type"? Do "types" of "type theory" semantically differ from "set" of set theory?

Algebraic transformation for dependent type

Is the opposite functor full and bijective on objects?

Prove that the class of well-founded sets is a proper class

Abelian-by-abelian group

For every closed set $C$, $f^{-1}(C)$ is closed. Is $f$ necessarily continuous?

sequence $2,10,18,26,$.... contains no cube

Algebraic formula for co-products in the category of digraphs

What is the name of a function that changes the sign of a number?

what is the speed of a divergent series?

Elevator pitch for a (sub)field of maths?

What Does the Associative Property Mean Intuitively Across All Notational Schemes?

Examples of (co)complete 2-categories that aren't (co)complete as a 1-category

Torus/ Thick Möbius Band homeomorphism

Is a constant such as 8 considered an expression?

Where is the value of the variable $\epsilon$ obtained in the following explanation my professor gave?

Is this a valid example for $f \circ g = id_M$, but $g \circ f \ne id_N$

Is there a geometric realization of Quaternion group?

Are these bases for a topology?

Powerset functor weakly preserves pullbacks.

Is a Lattice just a linearly ordered set?