Experiment with Semiringal and Ringal type classes, extending
Semigroupal and Monoidal.

Provide a [Cactus](https://cactuscode.org/) driver based on
[AMReX](https://amrex-codes.github.io), a software framework for
block-structured AMR (adaptive mesh refinement). This driver is
intended for the [Einstein Toolkit](https://einsteintoolkit.org/).

    echo y | sudo sh cmake-$version.$build-Linux-x86_64.sh --prefix=$HOME
    sudo ln -fs $HOME/cmake-$version.$build-Linux-x86_64/bin/cmake /usr/local/bin/cmake

    sudo sh cmake-$version.$build-Linux-x86_64.sh --prefix=$HOME/cmake --exclude-subdir --skip-license
    sudo ln -fs $HOME/cmake/bin/cmake /usr/local/bin/cmake

    which gcc
    which g++
    which gfortran
    gcc --version
    g++ --version
    gfortran --version

    pwd
    echo "HOME=$HOME"
    ls -l $HOME