SWI-Prolog -- assoc_to_keys/2

Documentation
- Reference manual
  - The SWI-Prolog library
    - library(assoc): Association lists
      - Conversion predicates
        
        assoc_to_list/2
        
        assoc_to_keys/2
        
        assoc_to_values/2
- Packages

Availability::- use_module(library(assoc)).(can be autoloaded)

Source

[det]assoc_to_keys(+Assoc, -Keys)

True if Keys is the list of keys in Assoc. The keys are sorted in ascending order.