Revert "Fix only mpi branch" on master branch

This reverts commit de4e10acded546c6adf3dd6d787930c02b29a24c.
Revert "Correct the structure of the intervals and of the base cases" on
master branch

This reverts commit 8770e2537c609966cc727a904009f0c3dc926eb6.
Revert "whap: First try only MPI" on master branch

This reverts commit 3c80428fba4c204d2195c8ebf6bced0beeb3f0ed.