# Xah Math Blog Archive 2014-10 to 2014-12

how many pieces can you get by cutting a donut 3 times? (you are not allowed to re-arrange the pieces after each cut)

rephrase: Maximal number of regions of dividing a torus with n planes? (n=3 here.)

“group theory” should be called “symmetry theory”

Math Terminology and Naming of Things

Hermitian matrix

In mathematics, a Hermitian matrix (or self-adjoint matrix) is a square matrix with complex entries that is equal to its own conjugate transpose—that is, the element in the i-th row and j-th column is equal to the complex conjugate of the element in the j-th row and i-th column, for all indices i and j.

Hermitian matrices can be understood as the complex extension of real symmetric matrices.

Symmetric matrix

In linear algebra, a symmetric matrix is a square matrix that is equal to its transpose. Example

```{
{1, 7, 3},
{7, 4, 5},
{3, 5, 6},
}```

Great Math Board Game Software (minor update)

sad to know. Alexander Grothendieck died 2 days ago. Alexander Grothendieck

geometric design on sphere. http://taffgoch.deviantart.com/

old goodie. State of Theorem Proving Systems 2008