Is the set $x^2-y^2 = 0, z > y \geq0 $ a smooth manifold in $\mathbb{R}^3$?
I think that the answer is no, but I'm not really sure how to prove this as I'm having trouble visualizing how it looks. Any help would be appreciated!
Is the set $x^2-y^2 = 0, z > y \geq0 $ a smooth manifold in $\mathbb{R}^3$?
I think that the answer is no, but I'm not really sure how to prove this as I'm having trouble visualizing how it looks. Any help would be appreciated!
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$\newcommand{\Reals}{\mathbf{R}}$Hints on visualization:
The equation $0 = x^{2} - y^{2} = (x + y)(x - y)$ cuts out a pair of planes in $\Reals^{3}$ that intersect orthogonally along the $z$-axis.
The portion where $y \geq 0$ is the (generalized) cylinder parallel to the $z$-axis lying over the graph $y = |x|$, i.e., a "trough" comprising a pair of half-planes intersecting orthogonally.
The portion where $z > y \geq 0$ is the intersection of the trough with the open half-space $z > y$.
Can you take it from here?