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Apr 4, 2022 at 12:38 comment added Sam Hopkins Sorry, I should have written "the half-plane $\{(x,y)\colon x \geq 0\}$" in the previous comment, of course.
Apr 3, 2022 at 17:22 comment added user332905 Ok. Thank you..
Apr 3, 2022 at 17:21 comment added Sam Hopkins In $\mathbb{R}^2$, the half-plane $\{(x,0)\colon x \geq 0\}$ has all of the line $x=0$ as apices.
Apr 3, 2022 at 17:20 comment added user332905 @SamHopkins Can you give an example of a cone with more than one apex?
Apr 3, 2022 at 17:16 comment added Sam Hopkins $C-a$ means the set $C-a := \{c-a\colon c\in C\}$ (this is like Minkowski sum notation). According to this definition, an example of a cone would be the open positive orthant $\{(x,y)\colon x, y >0\}$ in $\mathbb{R}^2$, which has apex the origin $(0,0)$, but the origin is not in the cone.
Apr 3, 2022 at 17:09 history asked user332905 CC BY-SA 4.0