“…The module REFINE refines all marked elements and perhaps a few more to keep mesh conformity. Of all possible refinement strategies, we are interested in bisection, a popular, elegant, and effective procedure for refinement in any dimension [48,8,32,33,55,3,49,54]. Our goal is to design optimal multilevel solvers that constitute the core of procedure SOLVE, and analyze them within the framework of highly graded meshes created by bisection, from now on called bisection grids.…”