Solution (source code)

= Solution

The curve-based <tangent space> at $x$ consists of velocities $\gamma'(0)$ of smooth curves $\gamma:(-\varepsilon,\varepsilon)\to M$ satisfying $\gamma(0)=x$. For an arbitrary subset these velocities need not form a <vector space>; for a smooth <submanifold> they do, and this is its usual <tangent space>. This definition suffices for the direct computation at the identity.