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2d
revised solving $f(f(x))=g(x)$
edited tags; edited title
2d
revised How to solve $f(f(x)) = \cos(x)$?
edited title
2d
awarded  Nice Answer
Feb
10
comment 2nd order partial differential equation with non-constant coefficients
@R. Bryant : I think that the change of variable leads to a more complicated equation, which includes some irst-order derivatives. Perhaps you should put a weight in $g$.
Feb
9
comment Unifying (& “justifying”) the various definitions for differential operators
This shows the gap between the topic of PD-Operators and that of PD-Equations. Up to some extent, these branches of mathematics ignore each other.
Feb
9
revised Duality argument to get $L^\infty-L^2$ inequality
added 156 characters in body
Feb
5
comment Is the Flajolet-Martin constant irrational? Is it transcendental?
I didn' know that MO could be used to offer money. Strange, since you can offer up to 500 reputation points through a bounty.
Feb
5
revised What is the probability that two random permutations have the same order?
added 18 characters in body; edited title
Feb
4
comment Elementary prime-generating sequences
Even simpler than Chow's comment : I heard once that we still ignore whether there are infinitely many primes of the form $n^2+1$.
Feb
4
comment Applications of Jordan algebras
added to YCor : consequently, one must pronouce Yordan', while Camille Jordan is pronounced Geordã.
Feb
3
answered Relation between eigenvalues of $A$ and $A^TA$?
Feb
1
revised Description of $\big(\ell^\infty(\mathbb N)\big)^{\!*}$ via ultrafilters
added 5 characters in body
Feb
1
answered Have you solved problems in your sleep?
Jan
28
comment Continuity + $H^1$ + Laplacian control $ \implies$ local Lipschitz property
When I answered the question, the assumption was pointwise, not away from a hypersurface.
Jan
28
answered Continuity + $H^1$ + Laplacian control $ \implies$ local Lipschitz property
Jan
26
awarded  Enlightened
Jan
26
awarded  Nice Answer
Jan
21
revised PDE characterisation of elementary symmetric functions?
added 16 characters in body
Jan
12
revised Frobenius complement/kernel of an infinite group
added 1846 characters in body
Jan
11
revised Number of turning points on a nondecreasing $n^2 \times n^2$ matrix
added 115 characters in body; edited title