“…Newer procedures may also be employed to improve the computed solution (see [5,13,14,32,33,35,37]). We point out, in particular, different versions of X-fem, PU-fem and G-Fem with or without (Heaviside) cut-off functions (see [2,9,10,36]). The reverse of the medal has to do with the condition number of the discrete problems to solve.…”