SWI-Prolog -- del_attrs/1

Documentation
- Reference manual
  - Constraint Logic Programming
    - Attributed variables
      - Special purpose predicates for attributes
        
        get_attrs/2
        
        put_attrs/2
        
        del_attrs/1
- Packages

Availability:built-in

del_attrs(+Var)

If Var is an attributed variable, delete all its attributes. In all other cases, this predicate succeeds without side-effects.