| SubOp
| SuperOp
-type attr_list = vvar list
+type vvar_list = vvar list
type set_exp = SVar of svar
| RVar of rvar
| Ref of val_exp
| Pattern of val_exp
- | Relation of refine_op * string * set_exp * attr_list
+ | Relation of refine_op * string * set_exp * vvar_list
| Select of rvar * set_exp * boole_exp
| Union of set_exp * set_exp
| Intersect of set_exp * set_exp