SWI-Prolog -- true/0

Documentation
- Reference manual
  - Built-in Predicates
    - Control Predicates
      - fail/0
      - false/0
      - true/0
      - repeat/0
      - !/0
      - ,/2
      - ;/2
      - |/2
      - ->/2
      - *->/2
      - \+/1
- Packages

Availability:built-in

[ISO]true

Always succeed. The predicate true/0 is translated into a single virtual machine instruction.