Typecases should be updated

[lovrolu]

Currently the MATN function tries to be clever and construct one of MAT{2,3,4} when it detects those dimensions.

This is ok by itself, however, the general versions of every (?) binary (?) operation (when the matrix is a MATN) assume that the second operand will also be a MATN, which won't be the case if you constructed your array using MATN since it might give you a MAT{2,3,4} instead.

As an example, the following will work if len is 2 since both p and q will be of type MAT2. However, it will fail if len is 3 since then p is a MATN and q is a MAT3, and M* doesn't handle this case.

(let* ((p (matn 2 len))
       (q (matn len len)))
  (m* p (minv q)))