// Apply symmetries to interpolated values
  assert(!reflection_x);
  assert(!reflection_y);
  assert(!reflection_upper_x);
  assert(!reflection_upper_y);
  assert(!reflection_upper_z);
  if (reflection_z) {
    // The code below is only valid for Psi4
    assert(nvars == 2);
    assert(varinds[0] == CCTK_VarIndex("Weyl::Psi4re"));
    assert(varinds[1] == CCTK_VarIndex("Weyl::Psi4im"));
    // l^a = et^a + er^a
    // n^a = et^a - er^a
    --

Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2902/carpetx-interpolation-with-z-reflection