Why isn't the graph of $y=|x|$ a smooth manifold?
11319
Is $M=\{(x,|x|): x \in (-1, 1)\}$ not a differentiable manifold?
97209
Smoothness of a surface
135059
Prove that the unit circle, $S^1:=\{(x,y)\in \mathbb{R}^2: x^2+y^2=1\}$, Is a one-dimensional manifold
72602
Why is important for a manifold to have countable basis?
151637
How do we prove that this set is not manifold?
133808
A doubt from Milnor's "Topology from a Differentiable Viewpoint".
84419
Product of manifolds & orientability
64920
Boundary Question in $\mathbb{R}^{2}$ (Manifolds)
65919
Sanity check about Wikipedia definition of differentiable manifold as a locally ringed space
107148
Does there always exist a continuous/smooth map from $\mathbb{R}^n$ onto a manifold $M^n$?
98845
Upper bound on the number of charts needed to cover a topological manifold
155060
Confusion about definition of manifold with boundary
102323
Nice neighborhoods of each "piece" in a manifold connected sum
76428
Exercise $2.1.1$ - Differential Topology by Guillemin and Pollack
51268
Why can't a Meredith Graph be Hamiltonian?
93986
Connectivity, Path Connectivity and Differentiability
124861
The extension of smooth function