For any number of holes, the formula generalizes to V − E + F = 2 − 2N, where N is the number of holes. The term "toroidal polyhedron" is also used for higher-genus polyhedra and for immersions of toroidal polyhedra. Automorphisms
The homeomorphism group (or the subgroup of diffeomorphisms) of the torus is studied in geometric topology. Its mapping class group ( the connected components of the homeomorphism group) is surjective onto the group GL(n, Z) of invertible integer matrices, which can be realized as linear maps on the universal covering space Rn that preserve the standard lattice Zn (this corresponds to integer coefficients) and thus descend to the quotient.
Retrobulbar bleeding, also known as retrobulbar hemorrhage, is when bleeding occurs behind the eye. Symptoms may include pain, bruising around the eye, the eye bulging outwards, vomiting, and vision loss.Retrobulbar bleeding can occur as a result of trauma to the eye, surgery to the eye, blood thinners, or an arteriovenous malformation.In those with significant symptoms lateral canthotomy with cantholysis is indicated. This is recommended to be carried out within two hours. The condition is rare. == References ==