I have a question regarding the notion of the tangentialcone used in nonlinear optimization.
Say we have a nonconvex admissible set $X$:
$X :=\lbrace x\in\mathbb{R}^2|x_1\geq0,x_2\geq0,x_1x_2\leq0\rbrace$
The tangentialcone at $(0,0)$ is then the whole set $X$ as far as I can understand from the definition, but $X$ is not a cone?