SWI-Prolog -- (@<)/2

Documentation
- Reference manual
  - Built-in Predicates
    - Comparison and Unification of Terms
      - Standard Order of Terms
        
        ==/2
        
        \==/2
        
        @</2
        
        @=</2
        
        @>/2
        
        @>=/2
        
        compare/3
- Packages

Availability:built-in

[ISO]@Term1 @< @Term2

True if Term1 is before Term2 in the standard order of terms.