# Determinant of block matrices

I need to calculate the determinant of a symbolic 4x4 matrix M, where each cell itself is a matrix itself.

Is that possible?

I did a beginner's check, and it did not seem to work:

```
mq=matrix(SR, 2, 2, 'a b c d'.split(' '))
MQ=matrix(SR, 2, 2, [mq, mq, mq, mq])
MQ.det()
Traceback (click to the left of this block for traceback)
...
TypeError: mutable matrices are unhashable
```

Hey, are you from Germany?