“…Another crucial property of VEM is that the space of the basic functions is associated with the PDE problem inside the element, thus it is convenient to define divergence-free or rotation-free virtual elements [18]. For a thorough description of the VEM, see [3,19,41]. The (divergence-free) VEM are used to discretize the Stokes problem [12,24,29,40,42], the Brinkman problem [33,44,51], the Navier-Stokes problem [25,56] and so on [21,28,30,43,53].…”