Papers dealing with solvers for saddlepoint problems (like the incompressible Navier-Stokes equations, [example](https://epubs.siam.org/doi/abs/10.1137/16M1076770)) usually define the block matrix as ```math M = \begin{pmatrix} A & B^T\\ B & C \end{pmatrix} ``` where $`A`$ is the block for the derivatives of the momentum balance equation residuals w.r.t velocity ("velocity block") and $`C`$ is is the block for the derivatives of the mass balance equation residuals w.r.t pressure ("pressure block"). For incompressible fluids, $`C`$ is zero. However, the multitype blockmatrix in Dumux for staggered problems looks like this: ```math M = \begin{pmatrix} C & B^T\\ B & A \end{pmatrix} ``` which causes confusion and requires special care, e.g, for the implementation of the Uzawa solver !1827 I suggest we adapt the matrix structure such that the velocity block is on the upper left. Are there any concerns / objections?