All X is Y but not all Y is X
125316
How would you define the relation between (for example) "Italian" and "languages"?
129677
Problem with Density of $X-Y$
154091
Is there any counterexample to show that $X,Y$ are two random variables and $E(X\mid Y)=E(X)$, but $X$ and $Y$ are not independent.
29653
Show that $xy=0$ is a variety but not a manifold
28822
$|x| - |y| \leq |x-y|?$
126862
Confused about $x \notin x$ example in Axiom of Specification
15238
subtraction of Y values
59577
Simple examples of uncorrelated but not independent $X$ and $Y$
40586
There exists an injection from $X$ to $Y$ if and only if there exists a surjection from $Y$ to $X$.
143735
Prove/Disprove: For any sets $X$ and $Y$, $\overline{X\cap Y} = \bar{X}\cup\bar{Y}$
150141
Showing $X$, $Y$ are not independent but $\operatorname{Cov}[X, Y] = 0$
93967
Prove partial derivatives exist, but not all directional derivatives exists.
84654
The graph of xy = 1 is connected or not
662
If $E[X|Y]=Y$ almost surely and $E[Y|X]=X$ almost surely then $X=Y$ almost surely
8094
X, Y, Z — horizontal, vertical and ...?
20658
Difficulty in finding a counterexample
33543
is "y1 < x < y2" an inequality or inequalities?