Any general rules as to when an affine space is a vector subspace and when it's not?
Because Wikipedia example:
says that in that case $P_2$ is not a subspace.
However the article gives in many parts that an affine space is a subspace. However, does this not even imply that it could be a vector/linear subspace in some cases?
The article also write:
Any vector space may be considered as an affine space
So this means that affine spaces can be vector spaces without the null vector property?