      void check_const_index(const unsigned int arg,
                             char *const ss, char *const se, const char saved_char) {
        if (arg!=~0U && !_cimg_mp_is_const_scalar(arg)) {
          char *s0; _cimg_mp_strerr;
          throw CImgArgumentException("[" cimg_appname "_math_parser] "
                                      "CImg<%s>::%s: %s%s Specified image index is not a constant, "
                                      "in expression '%s'.",
                                      pixel_type(),_cimg_mp_calling_function,s_op,*s_op?":":"",s0);
        }
      }
      void check_const_index(const unsigned int arg,
                             char *const ss, char *const se, const char saved_char) {
        if (arg!=~0U && !_cimg_mp_is_const_scalar(arg)) {
          char *s0; _cimg_mp_strerr;
          throw CImgArgumentException("[" cimg_appname "_math_parser] "
                                      "CImg<%s>::%s: %s%s Specified image index is not a constant, "
                                      "in expression '%s'.",
                                      pixel_type(),_cimg_mp_calling_function,s_op,*s_op?":":"",s0);
        }
      }