Implement the suggetion made here (https://github.com/MFlowCode/MFC/pull/821#discussion_r2052708379) for equation indices and the suggestion made here (https://github.com/MFlowCode/MFC/pull/819#issuecomment-2847058417) for `bcx[y,z]b[e]`.
Implement the suggetion made here (#821 (comment)) for equation indices and the suggestion made here (#819 (comment)) for
bcx[y,z]b[e].