User3060
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 Apr8 revised Subgroups of $GL(2, \Bbb{R})$ added 41 characters in body Apr8 comment Subgroups of $GL(2, \Bbb{R})$ That was a typo, I meant a proper subgroup of $GL(2,\Bbb{R})^+=\{a \in GL(2, \Bbb{R}):\ \det(a)>0\}$. Apr8 asked Subgroups of $GL(2, \Bbb{R})$ Apr6 comment $\mathbb{R}^2$ as a quotient of a group Thanks for the first example, but the second example is homeomorphic to the product of $\mathbb{R}^2$ with a singleton. Apr6 accepted $\mathbb{R}^2$ as a quotient of a group Apr6 comment $\mathbb{R}^2$ as a quotient of a group I fixed that! I meant as two topological sets they are homeomorphic. Apr6 revised $\mathbb{R}^2$ as a quotient of a group I replaces "in a bijection relation" by "homeomorphic". Apr6 asked $\mathbb{R}^2$ as a quotient of a group Mar1 accepted Transpose in ${SL}(2,\mathbb{R})$ Mar1 revised Transpose in ${SL}(2,\mathbb{R})$ edited tags Mar1 asked Transpose in ${SL}(2,\mathbb{R})$ Jul16 accepted Sum by twos for functions on $\Bbb{Z}$ Jul16 awarded Commentator Jul16 revised Sum by twos for functions on $\Bbb{Z}$ added 11 characters in body Jul16 comment Sum by twos for functions on $\Bbb{Z}$ by `sum by twos' I mean exactly the thing that brogrenkp said. And I fix the error in the question. Jul16 revised Sum by twos for functions on $\Bbb{Z}$ edited tags Jul16 asked Sum by twos for functions on $\Bbb{Z}$ Jul15 awarded Revival Jul12 comment Positive Semi-Definite matrices and subtraction @Martin Argerami: If $A=(a_{i,j})_{i,j=1}^n$ and $B=(b_{i,j})_{i,j=1}^n$ are two positive semidefinite matrices with real values and $a_{i,j}\geq b_{i,j} \geq 0$ for every $i,j$. Can we say anything about $A-B$? Jul7 awarded Editor