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22h
comment $-1$ as the only negative prime.
Small remark: even if it's extremely unusual, the great John Conway makes some interesting points on the interest of considering $-1$ as prime in the preface of The Sensual (Quadratic) Form. They may be a bit off-topic for the OP, but are worth reading nevertheless.
22h
comment Group of exponent $2$.
It is correct. In an Abelian group, "conjugate" is another name for "equal" so the property easily follows from the fact that exponent-2 groups are Abelian.
Feb
2
comment Finding char polynomial in $Z_3$
Your formula for the determinant looks suspicious... Sarrus's rule is only valid for $3 \times 3$ matrices → en.wikipedia.org/wiki/Rule_of_Sarrus
Jan
29
comment Theorem 2.27 (a) in Baby Rudin: Is his proof complete enough?
Always relevant: abstrusegoose.com/12
Jan
29
answered Are 3#4 and 3*#4composite knots isotopic?
Jan
29
asked What does it take to have a precise definition of volume?
Jan
6
comment Term for an infinite sequence with both a beginning and an end
I would call that a $(\omega + \omega^*)$-sequence, see e.g. mathworld.wolfram.com/OrderType.html. But I don't think a canonical name exists.
Jan
5
awarded  Enlightened
Jan
5
awarded  Nice Answer
Dec
18
comment Set consisting of all unoriented cobordism classes of smooth closed $n$-manifolds can be made into additive group?
Addition is disjoint union, inverse is the manifold itself.
Nov
20
awarded  Nice Answer
Oct
29
revised Alien Mathematics
edited body
Oct
28
comment Applications of the Hurwitz Theorem on Number of Automorphisms?
It's not really an application, but Hurwitz's theorem proves that not all points on a Riemann surface of genus $g \geq 2$ are equivalent (of course it's a very weak consequence of the finiteness of $\mathrm{Aut}(S)$). This is a massive difference between (real) differential geometry and complex geometry, and it's the first example of this phenomenon (on Riemann surfaces of genus $0$ or $1$, all the points are equivalent). One of the proofs of the theorem actually goes through the study of some particular points on the surface, the Weierstraß points.
Oct
23
awarded  Nice Answer
Oct
20
comment $A$ has $n$ distinct eigenvalues. Show that $C(A)$ is generated by elements in the form $A^i$ and compute its dimension
Are you familiar with the concept of diagonalisable matrices?
Oct
16
answered on the continuum hypothesis: only finitely many cardinals between $\aleph_0$ and $2^{\aleph_0}$
Oct
16
reviewed Approve Disproving $A-S-S(Angle-Side-Side)$ congruence condition…
Oct
16
reviewed Leave Open Is there something special about 2015?
Oct
15
comment Bijection between a set of subspaces and a set of vectors
What dimension should $U$ have? Can you think of a way to link a space of that dimension and a vector?
Oct
15
answered Smooth diffeomorphism and $C^1$ diffeomorphism