4 I am studying geometric measure theory, and I am having some trouble understanding how to deal with approximate tangent spaces. I would like an example/exhibition of an approximate tangent space in a regular setting (so that it does coincide with a classic vector subspace). First of all, the definition.
In mathematical notation, what are the usage differences between the various approximately-equal signs "≈", "≃", and "≅"? The Unicode standard lists all of them inside the Mathematical Operators B...