RIGHTFOLD        1325 lj_opt_fold.c      return RIGHTFOLD;
RIGHTFOLD        1384 lj_opt_fold.c      return RIGHTFOLD;
RIGHTFOLD        1539 lj_opt_fold.c      return RIGHTFOLD;
RIGHTFOLD        1554 lj_opt_fold.c      return RIGHTFOLD;
RIGHTFOLD        1860 lj_opt_fold.c      return RIGHTFOLD;  /* (b o1 a) o2 b ==> b; (a o1 b) o2 b ==> b */