SWI-Prolog -- get_flag/2

Documentation
- Reference manual
  - Built-in Predicates
    - Database
      - Flags
        
        get_flag/2
        
        set_flag/2
        
        flag/3
- Packages

Availability:built-in

get_flag(+Key, -Value)

True when Value is the value currently associated with Key. If Key does not exist, a new flag with value‘0’(zero) is created.