message: pre- appending the dollar sign to math equation
diff: This example solves a 2D Poisson equation:
  $
  - \Omega = (0,1)^2
  - \Omega_b = [0,1]^2 (with boundary)
  - \partial\Omega = \Omega_b \backslash \Omega
  - u : \Omega_b -> R
  - u'' = f in \Omega
  - u = u_D on \partial\Omega
  + \Omega = (0,1)^2 \\
  + \Omega_b = [0,1]^2 (with boundary) \\
  + \partial\Omega = \Omega_b \backslash \Omega \\
  + u : \Omega_b -> R \\
  + u'' = f in \Omega \\
  + u = u_D on \partial\Omega \\
  $
  using a finite difference method on an equidistant grid with `K` discretization
  points (`K` can be controlled with a command line parameter). The discretization
  may be done by any order Taylor polynomial.
  -For an equidistant grid with K "inner" discretization points (x1,y1), ...,
  -(xk,y1),(x1,y2), ..., (xk,yk,z1) step size h = 1 / (K + 1) and a stencil \in
  -\R^{3 x 3}, the formula produces a system of linear equations
  +For an equidistant grid with K "inner" discretization points $ (x1,y1), ...,
  +(xk,y1),(x1,y2), ..., (xk,yk,z1) $ step size $h = 1 / (K + 1)$ and a stencil $\in
  +\R^{3 x 3}$, the formula produces a system of linear equations
  -\sum_{a,b=-1}^1 stencil(a,b) * u_{(i+a,j+b} = -f_k h^2, on any inner node with
  +$\sum_{a,b=-1}^1 stencil(a,b) * u_{(i+a,j+b} = -f_k h^2 $, on any inner node with
  a neighborhood of inner nodes
  On any node, where neighbor is on the border, the neighbor is replaced with a
  -'-stencil(a,b) * u_{i+a,j+b}' and added to the right hand side vector. For
  +$-stencil(a,b) * u_{i+a,j+b}$ and added to the right hand side vector. For
  example a node with a neighborhood of only edge nodes may look like this
  -\sum_{a,b=-1}^(1,0) stencil(a,b) * u_{(i+a,j+b} = -f_k h^2 - \sum_{a=-1}^1
  -stencil(a,1) * u_{(i+a,j+1}
  +$\sum_{a,b=-1}^(1,0) stencil(a,b) * u_{(i+a,j+b} = -f_k h^2 - \sum_{a=-1}^1
  +stencil(a,1) * u_{(i+a,j+1}$
  which is then solved using Ginkgo's implementation of the CG method
  preconditioned with block-Jacobi. It is also possible to specify on which
  executor Ginkgo will solve the system via the command line.
  -The function `f` is set to `f(x,y) = 6x + 6y` (making the solution `u(x,y) = x^3
  -+ y^3`), but that can be changed in the `main` function. Also the stencil values
  +The function `f` is set to $f(x,y) = 6x + 6y$ (making the solution $u(x,y) = x^3
  ++ y^3$, but that can be changed in the `main` function. Also the stencil values
  for the core, the faces, the edge and the corners can be changed when passing
  additional parameters.
  