SWI-Prolog -- copy_term_nat/2

Documentation
- Reference manual
  - Constraint Logic Programming
    - Attributed variables
      - Operations on terms with attributed variables
        
        copy_term/3
        
        copy_term_nat/2
        
        term_attvars/2
- Packages

Availability:built-in

copy_term_nat(+Term, -Copy)

As copy_term/2. Attributes, however, are not copied but replaced by fresh variables.