I know that $\frac{(x-h)^2}{a^2}-\frac{(y-k)^2}{b^2}=1$ or $xy=c^2$ or $x^2-y^2=a^2$ represents hyperbola. But I came across the following equations that according to desmos and wolfram are hyperbola. I wonder what their general form is. $\frac1x+\frac1y=-\frac2{37}$ (wolfram) $y=\frac{x-1}{x+1}...

Steinhaus Property: A subset $A$ of $\mathbb{R}$ is said to have Steinhaus Property if $A-A$ contains an interval around the origin. Weak SteinhausA subset $A$ of $\mathbb{R}$ is said to have Steinhaus Property if $A-A$ contains an interval. Does Weak-Steinhaus imply Steinhaus? Countable Sets ar...

I have noticed that the standard Cantor Set which has measure $0$ nonetheless has the Steinhaus Property ($A-A$ has non empty interior around $0$). On the other hand for any countable set $A$, $A-A$ has empty interior. My question is: Is the class of measure 0 sets with Steinhaus Property intere...