For $x\in\operatorname{Ext}_R^1(C,A)$, how to construct an extension $0\to A\to B\to C\to 0$ such that $\partial (id_A)=x$?
113708
Correspondence between Ext group and extensions (from Weibel's book)
95774
$\frac{\partial^2 u}{\partial t^2}-c^2\frac{\partial^2u}{\partial x^2}=0\text{ implies } \frac{\partial^2 u}{\partial z \partial y}=0$
147069
Intersection of field extensions
119684
Is a contraction idempotent operator self-adjoint?
77891
$(U\circ T)^{*} = T^{*}\circ U^{*}$
21923
Prove that $\exp(x)>0$ using only formal definition of exp
123197
$C^2 $embedded in holder space?
39380
How do I visualize $\exp(z)$ as a complex mapping?
63473
Is the shorthand $ \partial_{\mu} $ strictly a partial derivative in field theory?
55488
Proving that $\operatorname{codim}(X,Y)=\dim(\mathcal{O}_{X,\eta})$
46825
The identity det(A) = exp(Tr(ln(A)) for A general
128911
Continuous extension of a real function
50664
Inverse function of $\operatorname{li}(x)$ over $x>\mu$?
156597
Proving a reduction formula for the antiderivative of $\cos^n(x)$
150274
Inverse of a function - $f^-(x)$ in a restricted domain
147659
Counterexample to "if $f:A\to A$ induces the identity $\hat f:\operatorname{Spec}(A)\to\operatorname{Spec}(A)$, then $f=\operatorname{id}_A$"
153886
Existence of antiderivative on a part $I$ of $\mathbb{R}$