sponge := proc(a,b,c,L,v,m) 
  description `returns the Menger Sponge`;
  local p,np,i,j,k;
  if v = 0 then
    p := [plottools[hexahedron]([a,b,c],L,style=line)]:
  else
    p := []:
  end if;
  for i from -1 to +1 do
    for j from -1 to +1 do
      for k from -1 to +1 do
        if abs(i) + abs(j) + abs(k) = 1 then
          np := plottools[hexahedron]([a+2*i*L/3,b+2*j*L/3,c+2*k*L/3],L/3):
          p := [op(p),np]:
        end if;
      end do;
    end do;
  end do;
  if v < m then
    for i from -1 to +1 do
      for j from -1 to +1 do
        for k from -1 to +1 do
          if abs(i) + abs(j) + abs(k) > 1 then
            np := sponge(a+2*i*L/3,b+2*j*L/3,c+2*k*L/3,L/3,v+1,m):
            p := [op(p),op(np)]:
          end if;
        end do;
      end do;
    end do;
  end if;
  return p;
end proc;